I am level 5, 4 and 3, because of 3 teams, so i think i can qualify to talk.

Until nevel 3 i just used always the same formation, because you always have a lot of abandoned teams, playing ilegal formations.
In my first Team level 1 and 2 played 343, then After that i play mostly 442, but change it to counter similar Q oponents.

In my level 4 Team i change tactic, but i always play with 3DC, so use 352, 3412, 3142, 31411, and until now this has Been the most efective, Never won the league but won one cup and was 2nd in CL.

In the other i normally use 442 assymetrical, worked very well in level 1 were i was champion with 10 points ahead of 2nd. But i normally only use this one to play friendlies.

I think i always good to counter the tactic of your oponent, but is also important to play with your Best player and fit them in a tactic were they could play better. Sometimes playing with a player or 2 out of position it is not bad.
I have a ML that in is position always had low ratings, then i had to put him as MC, and he played so good i just keep him playing on that position.
I had a DMC that one season playing as DC was MOM 3 times in the season.

Orders can also be a important part in the game, but it is really hard to understand how they can influence the game.