The majority of people online probably know less about football than you do but they are good at madden which is mostly exploits. There's meta plays for offense and defense. The trick is to know what beats those plays but it's often countering cheese with cheese. I would suggest joining an online Franchise that plays a more realistic style of football.
But playing H2H I would suggest getting really comfortable with one formation and have several runs and passes out of it and mix it up to keep opponents guessing. And play the game at your own tempo. Dictate the pace. I like to run and use the clock to limit possessions by the opponent since most people online like to have a quick scoring offense going for big plays. Also since games are so short there's only a few possessions per game. You could realistically keep the ball for an entire half.
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