A lot of good formations. Get your best players on the pitch is the usual best answer.

I enjoy the 4-1-2-1-2. Good mix of defensive ability and offense.
If I want to attack wide and sacrifice some defense I've gone with 3-1-2-3-1.
Scout out your opponent, and see what works best for you!

Won 2 League titles in 3 seasons, as well as 1 CL.
Just starting to find out more about this game.

But getting very good players through auctions is pretty important.
Higher quality teams makes all your tactics better.