Vladimir, a true blood-sucking horror. This guide will tell you how to make use of his incredible powers, and claim victory for your own.

Greater Mark of Insight - Used for that oh-so-useful magic penetration, primarily early-game, when magic resist is still low, and shields a lot of damage.
Greater Seal of Shielding - Used for defending against the enemy's AP damage.
Greater Glyph of Potency - Used for damage throughout the game.
Greater Quint of Potency - Used for damage throughout the game.

21 points in Offense and 9 in Defense allow Vladimir to be a very dangerous foe, while sustaining a lot of damage.

I always like getting that early Kindlegem for early spamming of Transfusion and Tides of Blood, then later upgrading it to Spirit Visage for a lot of spell vamp, especially with the Hextech Revolver. A late-game Lich Bane also helps deal massive burst damage to those little rascals who happen to survive your other attacks.

Always try to max out Transfusion first. this helps out a great deal of Vladimir's damage, not to mention the extra healing.
Then I usually add a lot of points to Tides of Blood, since that's also a big damage factor.
Make sure you get an early point on Sanguine Pool, for this will enable an escape route if necessary.
ALWAYS get Hemoplague (Ultimate) as often as you can. This is very important for team fights and fighting in general.

Ignite - A common tool for most AP Carries, as it helps catch escaping foes.

Flash - A spell which should be used for almost any role of the team, it is a very valuable escape tool.

Cleanse - I've seen some Vladimirs use it before, but I don't recommend it.

Exhaust - Usually used with support or AD Carries, this wouldn't be as much of use as Ignite for Vladimir.

Clarity - Ok, no. If you really think Vladimir will ever use this, stop playing him. He doesn't even use mana.