There are two approaches. First you can adapt your tactics based on the players you have in your team. Or, second you have a tactic in your mind and you'll buy the right players for your tactic.
You have to specify what team you've managed, which players. Your formation will work best if you have at least one good advanced playmaker, one good pacey winger with good dribbling and crossing, one good inside forward with good dribbling and finishing and one good lonely striker.
I have the second approach. I form my team around my formation and tactic. I always buy very fast player, maybe not the best, but realy fast and pacey. I prefer:
formation: 4-1dm-1cm-2wingers-2strikers
mentality: attacking
fluidity: very fluid
team instructions: more direct passing, hassle opponents, use offside trap, higher tempo
I don't give a **** about possession, about controlling the game. My team is aggressive, making pressing on the enemy half, trying to capture the ball from their defenders, preventing enemy's midfielders to combine or to play the ball. When my team has the ball it try to pass quickly to strikers (a poacher - target man partnership) and they will shoot on the goal. Usually after three, four passes the shoot will come. Because my players are fast, they can catch any team on counter-attack. My defense stay relative high to compress the enemy on their half. My full backs are very present in attack, always being ready to cross or through the ball. My center backs are instructed to pass directly. Both my dm and cm must have good stamina, usually they will be overwhelmed in the middle of the pitch. DM have to be pacey, CM should be an advanced playmaker with good marking and tackling. Both wingers are used as wingers for crossing a lot to both strikers. They must be very fast because my defense line will through ball forward and they must catch them, or they have to surpass the opponent's full backs. Usually I start with both set them with "Cross Aim Far Post". If I see that all those crosses are stopped by tall center backs, I changed to "Cross Aim Near Post".
My main strength is the attack. I always can mark more goals than opposition, two strikers, two wingers and one midfielder can score any time. Even my enemies (the strong ones) can score twice against me, my team succeed to score 3 or 4 and I win.