Skills to consider on thralls
Block, Tackle
1 Kicker
1 or 2 Dirty Players (If you have no qualms about kicking people when they're down)
A couple of Sure Hands Thralls are decent to retrive the ball and transport it till it's time to give it to a vampire, but some people prefer to use vampires as ball carriers. Myself I like to use thralls as much as possible to spread SPPs.
Doubles: Guard and Dodge.
Vampires:
Block, Pro, Mighty Blow, Dodge, Tackle, Side Step. etc You can pretty much turn a Vampire into anything you want, concentrate on Block and Pro first. If there's not a lot of Tackle in the league Block, Dodge can be pretty good. Personally I get a mix of them.
Some other choices depend on the rules. I'll assume LRB 4.0.
Doubles: Stand Firm, Frenzy
In PBBL doubles on a vampire are pretty much wasted.
Because you tend to only field 3 Vampires max you have a unique situation where it's possible to tailor your vampires into offensive and defensive vampires. My starting Offensive vampire skill choices are Block, Pro and defensive ones are Block, Dodge.
I'm sure others will have more to add.
A big help with vampires is to always have a plan in case of blood lust, move a thrall first if it's important to get a vampire in a position (BL action can then go bite the thrall.) And don't forget about Hypnotic Gaze, it can often be used to provide 'fake blitzes' by removing key tackle zones and open a path. HG imo is the most potent weapon on the Vampires.