You need to be able to adapt your formation to counter your opponents formation. Players with duel position are vital to achieve this and also give you maximum cover from the bench with the least number of players.
Most managers at level 1 and 2 and even three in some cases use the generic formations that are available on the formations board. This is because they do not know how to use the counter and deploy technique.
While countering your opponents attack you need enough players left over to form your own attack.
It is important that you never have less MF players than your opponent, it's better to have at least one more if possible.
MF players are DM, MF and AM players. Always have one more defender than he has ST and AM players.
No formation is good if your opponent counters it.
No formation is guaranteed to win a game even against weaker teams, because the game engine is random.
All you can do is limit your opponents chances of winning and increase your own by exploiting your opponents weakness, the rest is down to gaining the best possession bonus and hope the game engine is kind to you.
Learning to counter and deploy will achieve better results than just putting your best 11 players on the field.
A 2* player with good form 77777 will perform better than a 3* 66576.
Many games in my league at level 3 MOM is awarded to 1* defenders against my 4* ST even if the score two goals against them, this is were the game engine evens up quality and turns games you should win into losses or draws against poorer teams. likw when top of the league get beat with a bottom four club, just as in real football, **** happens.