As much as you want. Firstly, just check basic match stats, that can tell you a lot - if your possession is low, there's something wrong with midfielders, formation, playing style or something. If you don't have many shots your players don't create enough chances, check your midfielders and forwards. If you have many shots but most off target, you're shooting too much and probably from too far away, instruct your players to work the ball into the box, not to shoot on sight... You can play successfully just by monitoring these stats. Next thing to note is of course players' ratings, which you have to monitor during the game. It warns you, if you're using a player in the wrong position or if you don't get everything you could out of him. If you want more, you can take a look at detailed match stats, action zones, analysis... That's all during the match. Before the match, scout the opposition, prepare for their tactics and plan your strategy, if you know their strong and weak points. During half time, read assistant's report, check the ratings and make any necessary changes. After the match, I always check post-match analysis to see all the shots, both mine and opposition's.
You can learn a great deal by looking at all these stats, but you can play just by looking at basic match stats. Everything together might seem complicated, boring or time consuming, but it is not.
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