You can basically ask us before buying but here's a little summary from my own experience :
1) Lawnmower blenny goes with everybody. Reef safe.
2) Clowns single species (a pair is ok but has to be different in size) unless your tank is big then you can have 2 species. Reef safe.
3) Tangs can be kept with other fishes but better not with their own species unless you have a big tank. Reef safe.
4) Angels and pygmy angels are not reef safe but they demand good water quality. Best in matured tanks.
5) Wrasses are cool with everybody.
6) Triggerfishes are the big bad boys of the tank.
They eat anything including your fingers.
7) Damsels are better left at the LFS since you'll try to get them out eventually.
Anybody else please add to this list. Cheers.