though I'd say I have a good general tactic knowledge I must say I suck at this game

There are so many sliders I dont know how to put them.
I'm going to play a team with good CM's that are good at passing - +15 passing. I don't know which yet, Arsenal would be a good team to begin with, but I dont want to play with a big side. Oh im going to make use of a 4-3-3 formation(2 wingers 2cm 1dm 1striker then pretty much a regular 4 man defense line)
I think I could figure out instructions for the CM's, wingers and strikers. But I wonder what instructions I should set on the CB's, GK and DM, and how to best make my fullbacks to assist midfield in order to gain more possesion? I just want to know that, not a full tactic because I like to think for myself as well

Leaking goals is the problem I'm having
Would appreciate a lot if somebody could help me out