If your deck mostly emphasizes on the creatures' effects then you need to add cards that will keep them
alive in combat, allow for them to reuse their effects and/or come back from the grave. However, if you're just going for the theme of vampires and you want the spells to do most of the work then make sure that they have long standing effects. Deck ratio wise I suggest starting the deck out with a little more than a 3rd of the deck being mana (this way it cuts down on mana droughts if you don't have the mana ramp going).The creature to spell ration depends solely on how you want to run the deck. I'd say 35% mana, 35% creatures, and 30% spells. Adjust this accordingly based off your play style. I always use more than 60 cards in a deck because I don't like using the minimum (but i never go over 70 cause that's too much in competitive play). But if it's mono vampires you want then shape up the deck based off the effects you're trying to use most often. For example, in my Esper (U/W/B) standard vampire deck I use black vampires and white kor allies. Though i had two creature types mostly and three colors I kept to the theme of
kalastria healer with
nirkana assassin,
bloodbond vampire, and
malakir familiar accordingly. I also combined these creatures with
retreat to hagra,
tandem tactics,
pathway arrows (because a deathtouch creature dealing creature damage to another creature is still deathtouch damage even when using an artifact or enchantment to do so). So no matter what colors you choose, make sure the spells help the creatures or have the two work in unison.