On your line up screen you have the option to save about 4 formations, i think. I always set up my tactics 12 hours minimum before the match.

He played a 4-1-4-1 and lost, he needs something more attackive.
As for your best player, unless he has a special ability, he wont have much affect in the game as nobody is up against him.

My best player is my defensive midfielder and i only use him to counter attacking mids.