Longbeards
a Longbeards job is to block. Guard is pretty much the 1st skill you give them. Sometimes, I alternate between Mighty Blow and Guard. Personally, I don't like Dirty Player, but it is a valid choice also. On Doubles, take stand firm or dodge or sidestep...all three are decent choices and allow the LB to stay in the middle of things.
Fun choice: Pass Block...it can give these slow players some mobility
Blitzers
Depends on what you plan to do with them. Mighty Blow and Guard are usually my 1st choices. I'd rather take Strip ball than tackle, as I already have tons of tackle on the team. On Doubles, Stand Firm, dodge or catch...(they are agility 3 you know)
Slayers
Mighty Blow 1st. Then things like guard, strip ball or takcle. Stand firm or Sidestep on doubles (keeps you from getting pushed out of bounds).
Very Fun Choice: Multiblock...yea, it's hard to use, but just the threat of it's use will make your opponent think twice about standing 2 players next to each other.
Runners
Block. They are the only members of the team without it..no reason to let that be true for long. After that, it all depends on what you want to do with them. I like having at least one passing runner and one blitzing runner. Contrary to popular belief, dwarves can do well with a short passing game once developed. Dump-off is another interesting choice. On Doubles, take dodge or sidestep.
I, personally, like the block/dodge combos--even on the agility 2 guys--because it means my players will stay standing more often. Yes, Tackle does negate dodge, but not everyone takes tackle with every player....
Kick is a good skill to give one player on the team. Probably a runner