1. To drink blood, use the Bite Victim ability. Remove their headgear first.
You must remain still while draining blood.
2. Danger! If you walk in space, starlight will burn you to a crisp.
The chaplain is your nemesis. Avoid him and the chapel.
3. New powers unlock when you collect a certain amount of blood (as indicated below). Every time you use a power that isn't free, it depletes part of your blood reserve.
40 - Bat Form, consume stamina to morph into a bat.
40 - Enthrall / Thrall Speak, revive a dead human as an enthralled servant.
300 - Coffin Escape / Mark Coffin, escape to a coffin to regenerate.
300 - Vampiric Vision, thermals.
600 - Frost Bats, defensive spell.
600 - Chiropteran Screech, stun people, break glass.
900 - Diseased Touch, give someone grave fever.
900 - Bat Form cloaks in dark areas.
1400 - Chiropteran Screech, breaks nearby radios.
1800 - Full power, no harm from chapel.
For more information, consult the wiki