Muktol

I have done a revision of the 'Vampire Onslaught' deck that was released with Innistrad. (http://www.mtgvault.com/muktol/decks/vampire-onslaught-revised/)

Some suggestion based on the deck mentioned above and my own R/B vampire deck:
Personally I hate to see that legality get's messed up by a single card. If you play the deck only at the kitchen table that might be OK, but perhaps you someday want to take your deck to a local tournament and then this will cause problems. Especially if you don't play them as 4 times but only twice, like "Dark Ritual" here.

The basic question is 'how do you want your deck to behave'? There are some possible ways for vampire decks: agro (control), combo, mid-/lategame. The most common will be agro and I will refer my suggestion on that.
"Blade of the Bloodchief" is an extremely good equipment for vampires. Every equipped vampire will get 2 +1/+1 counters when something dies, and that for only {1}+{1}
I would also include some additional removals as vampires (like many tribals) normally need support to make them effective. "Gatekeeper of Malakir", "Dismember", "Go for the Throat", "Tragic Slip" or "Doom Blade" would be the basic choices, but you also could take some discard like "Distress" or "Duress"
Last, I would take a look at some carddraw/ library manipulation spells. The best choice here would be "Read the Bones" or "Viscera Seer". This allows you to ensure that "Vampire Nocturnus"'s ability will be active when you need it to. Shuffling lands that you don't want to draw under you library is always a welcome option.

Now comes the question what to remove.
I would sideboard/ remove the following cards: "Blood Artist", "Child of Night", "Quag Vampires", "Exquisite Blood" and "Sanguine Bond". The enchantments belong more into a combo deck, while the rest is either to situational (many creatures have to die) or just to expensive (multikicker)
"Malakir Cullblade" might have a future when combined with "Blade of the Bloodchief" but the chances of drawing those two cards and then have a removal on my hand to activate it would be rather low.
I would also remove 2 of the 4 "Bloodline Keeper". He has the same mana-costs as "Vampire Nocturnus" but when having a Nocturnus and a Keeper on your hand you always want to play the Nocturnus in this deck.

Greetings
Muktol

"Lightform": The casting of this spell (one colorless and two white mana) counts for prowess.
The 'manifest' ability reads like this: "To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.". So the card you manifest isn't cast it's just put into play, thus no activation of prowess.

"Myth Realized": The casting of this spell (one white mana) counts for prowess.
The first ability puts a lore (not a +1/+1!) counter on the enchantment. It's an ability and thus doesn't count for prowess.
The second ability changes the type of the card from enchantment to creature. It's an ability and thus doesn't count for prowess.
"Myth Realized" is already on the battlefield, it just changes it's type, so no "enter the battlefield" effects will be activated.

If you want to know more about casting spells, ability's in general, special ability's like deathtouch and so on (prowess wasn't added when I recently checked), you should take a look at the complete magic rules book.
There are 2 different versions, one short version for beginners (http://media.wizards.com/images/magic/resources/rules/EN_MTGM14_Rulebook_LR.pdf) and a full version for all those who want/ need to dig deeper into the rules (http://media.wizards.com/images/magic/tcg/resources/rules/MagicCompRules_20140601.pdf).
Both links belong to a PDF file from the official magic website. The link to the site would be http://archive.wizards.com/Magic/tcg/article.aspx?x=magic/rules

Normal equipment decks are trying to be as fast as hell, because they can be overwhelmed rather easy by big creatures or mass-decks. So the question will be 'how fast do I want to play this deck?'
A good equipment will give you +x/+y for x+y mana (play and equip). For example "Bonesplitter" gives +2/+0 for {1}+ {1}, Shuko gives +1/+0 for {1}+ {0} and "Bone Saw" gives +1/+0 for {0}+ {1}. If you rely on getting a creature equipped (preferably with something offensive) I wouldn't only play 1 good equipment but try to get some more. Personally I would remove "Avacyn's Collar" and sideboard "Basilisk Collar" to get some more aggressive equipment's in. Plating also depends on how many cheap/ fast equipment/ artifacts you got in your deck. Plating equipped on an Ornithopther can easily kill your opponent (even if it might take some time without further support)

*like*
I'm missing some of the good (and not that expensive) cards and equipment's:
Cranial Plating (~1,3$ /card), Bone Saw (~0,2$ /card), Shuko (0,4$ /card), Swiftfoot Boots (0,5$ /card)
"Dispatch" (~1,3$ /card) can be a real good removal here.

Greetings
Muktol

Why not use "Kiln Fiend" or "Nivix Cyclops" when playing within modern-legality?
I would put "Twisted Image" into the sideboard because most of the creatures in magic have symmetric power and toughness. If it's for the cantrip, there are other cards you could use here, just do a quick cardsearch for 'text' + 'draw a card' + red + blue

Greetings
Muktol

Lightform will trigger prowess, as well as Myth Realized will, when it enters the battlefield. But that's it then.
Myth Realized gets a lore counter whenever you cast a noncreature spell and you then can pay {W} to tun it into a creature until end of turn, but the 'transformation' itself won't trigger prowess effects.
The same is true for the card manifested with lightform. You activate the ability of the face-down card, gained by lightform. But thats an ability and no spell is cast here.

Why do you think "Myth Realized" would trigger prowess?
Prowess is activated by non-creature SPELLS, activating "Myth Realized" uses its ABILITY, big difference. So the only time this card triggers a prowess ability is when it's cast, and thus enters the battlefield.
Worse, activating wouldn't even trigger enter the battlefield-effects because the card is already on the field. It just changes it's form.

OK, so the target is a standard R/W agro deck that focuses on prowess. Removing the U (blue) part may have lowered the chance of getting through your opponents defenses but we will take a look at that.

First I would change some numbers:
+1 "Bloodfire Expert"...good and aggressive, especially when combined with evasion or trample
Sideboard "Seeker of the Way" and increase to 4...I don't know the decks that re around standard at the moment but lifgain is an option I would always put into my sideboard and use when needed.
Remove "Student of Ojutai"..."Seeker of the Way" is the better choice here and were putting that one into your sideboard
+ 1-2 "Zada, Hedron Grinder"...tough the copies don't count for the prowess ability he's still a very strong supporter. Legendary, though don't use more than 3 of him in a deck.
That would be it for he creatures, now to the support spells.

I would concentrate on some cheap buff and protection spells here, and perhaps some removal.
+ 1-2 "Artful Maneuver"...with rebound it fits perfectly into a prowess deck.
-1 "Kindled Fury"...to get room for "Defiant Strike"
+2 "Defiant Strike"...+1/+0 doesn't sound to good but it allows you to draw an additional card and that can be worth it
-1 "Temur Battle Rage"...finisher, 3 should be enough
+1 "Titan's Strength"...best cheap buff spell red has to offer at the moment
-2 "Trumpet Blast"...I would concentrate on cheap spells that buff one creature.
-1 "Lightform"...lifegain, either remove or sideboard
-1 "Myth Realized"...with only one copy it's not consistent enough. If you draw and play it e.g. on T4 it will be hard to make a valuable 'creature' out of this. Also it doesn't benefit from prowess
+ 1-3 "Feat of Resistance" or "Center Soul"...protection will always be important. One the one hand you can protect your creatures from getting shot away, one the other hand you can help them to get through your opponents defense. A creature with protection from white can't be targeted by white spells (this also counts for your own spells) but it also cant be blocked or damaged by white creatures your opponent controls!

I hope I was able to help you a little bit.

There are millions of different decks out there and the answers for your question depend on some points:
What legality do you want this deck to be built for? At the moment it's nearly standard, the only card ruining that would be "Izzet Guildgate". if you want to play on a beginners tournament or FNM then it will have to be standard legal. If you want to play with your friends then it will either be modern or 'use what you have' aka kitchen table. Should this deck be competitive or do you just want to play with your friends?
What strategy do you want this deck to have? At the moment it looks like an aggressive and fast built that focuses on the 'prowess' ability of many creatures.
Are you willing to buy/ trade for new cards and what is the budget for new cards (per card or for all cards)?

And last, have you already played this deck and ran into some problems with it? If yes, what where those problems.

A short description and some details on what you need help with would be nice. Strategy, legality, budget and so on.
Also some deck-tags, including e.g. "Help", would be helpful.

Greetings
Muktol

*like*
Some suggestions/ Ideas:
When playing "Æther Vial" use a whole playset. A single one won't do much because the chances of drawing it at the beginning of the game are extremely low, so no real consistency. And if you draw and play it e.g. T3+ it will become pretty useless because it takes some time to get it to 3 counters (your ideal number for this deck) and that's a time you normally don't want to wait.
Personally I'm using "Vines of Vastwood" or "Ranger's Guile" to get a little bit more protection from removal.
If you want an alternative for "Burst Lightning" you could take a look at "Searing Blaze".

Greetings
Muktol

*like*
Why no "Assault Strobe"?
If you don't need the cantrip I would change from "Dragon Mantle" to "Madcap Skills".
And just for information (I'm sure you will know this, but others who might look at this deck might not) using "Steeling Stance"' forecast won't trigger heroic as it's a ability and not a casted spell.

Greetings
Muktol

Looking good for me now :)

Well with the mana-costs that low you can drop to 20-22 lands. If you need more cc1 spells you could also take a look at "Wolfbitten Captive" or "Young Wolf" (which I prefer over the Captive due to it's undying)

I would sideboard it and add either "Ranger's Guile" or "Vines of Vastwood". All other werewolf's are a 100% need as every one is vital and supports your strategy. If you really want to keep it try to reduce the number of lands to 22 and use 2-3, even if that means going above 60 cards
Vines has the advantage that you can target your opponents creatures too and thus 'counter' a spell he wants to cast on it. Also +4/+4 for a second {G} isn't too shabby. Brings your "Kruin Outlaw" on rampaging 14 damage without any further buffs.
Guile costs less ($) and will be easier to obtain.

From my experience playing (mostly against) werewolf's I can conclude that these decks normally finish their opponent with one hefty attack (30+ trampling damage within one turn is not unusual). Flyers are normally rather slow and weak so from my point of view I would rather take some beating from flyers and protect my creatures from my opponents spells rather than shoot down those creatures and perhaps have nothing on my hand against a Lightning Bolt or Doom Blade.

I would do some changes at numbers and cards:
- 1-2 "Instigator Gang"...finisher tough 1-3 ought to be enough.
+ 1 "Kruin Outlaw"

Change from "Brimstone Volley" to "Searing Blaze"...costs less (cmc) and is more effective in damaging your opponent's creatures and him self.
Change from "Incinerate" to "Lightning Bolt"...see above. You can always sideboard these spell if you feel that your opponent uses too many regenerating creatures.
Sideboard "Daybreak Ranger"

Some further suggestions:
"Vines of Vastwood", "Ranger's Guile", "Young Wolf"

Greetings
Muktol

Some suggestions:
"Cloudfin Raptor"...Can be a pain in the ass for your opponent. With this deck I will evolve onto a 2/3 flyer most of the time before your finishers hit the deck.
"Forced Adaptation"...allows you to place a +1/+1 counter on the enchanted creature at the beginning of every turn.
"Bioshift"...If you opponent uses some removal spells this will allow you to shift counters from a doomed creature onto another one.

I would lower the number of finishers a little bit, 3 types of hydras and Nylea, all in all 13 creatures only as finisher seems a little bit too much for me. You could add some protection or carddraw spells instead.

"Gyre Sage" won't evolve to often (once if you don't manage to play Nylea) before your finishers will hit the deck and thus the ramp you will get from it will be pretty low. If you want to get some ramp would take a look at cards like "Llanowar Elves" or "Rampant Growth".

A short deck description (budget, strategy and so on) and some deck-tags would be nice. It helps us to help you.

Greetings
Muktol

I would remove "Temple of the False God" because it's the only card that messes up your modern legality.

There would be another version of ramp that also can help you to avoid getting damage: Defender ramp. The key cards for this would be "Axebane Guardian" (~0.14$ per card) and/ or "Overgrown Battlement" (~0.20$ per card). I have used this method in a G/W angel deck and a good starting-hand allows me to play nearly any angel (even cmc 8 Avacyn) on T4+

Cards like "Utopia Sprawl" can be very effective in combination with some 'untap' creatures.
Depending on how many spells you and/ or your opponent can cast per turn "Scorned Villager" could also be worth a look.

If you need some protective spells take a look at "Ranger's Guile" (~0.12$ per card), "Vines of Vastwood" (~1.20$ per card) or "Withstand Death" (~0.15$ per card).

An alternative win option for you could be "Helix Pinnacle" (~6.50$ per card) (or "Door to Nothingness" (~1.23$ per card) if you manage to get the 5 colours together)

Greetings
Muktol

Well depending on how fast you are "Elusive Spellfist" or "Wingcrafter" could be an option.
Your creature choices demand rather fast and aggressive artefacts.