Besides the experience factors, you will also be able to unlock packs of cards using uncommon or elite status that will surely rank up your team degree and so performance. So on each subsequent leveling up of the MUT level, you get rewards with Mut 20 coins. These start with a small quantity of MUT coins which you can spend in the store to coaching packs to full elite and premium player packs.
Within these rewards will also be special cards known as power packs. What they do is increase the stats of a certain card by some points. As you unlock more levels, you'll get more power packs that will rank up your stat degree on the cards even higher up, up to 90 even. Do notethe climbing goes up each time you level up, which makes it considerably more difficult to level up on high levels, so that needs a bit more grinding.
Additionally, there are flat caps, so you won't be able to max out on solo challenges if you simply stick to a single degree of difficulty. That is the reason why, it is most useful if you can bring yourself to be able to handle the challenges of a tougher A.I etc..
Solo battles also work, as they can reward you some good XP without taking on some unpleasant CPU competitions. Difficulty is quite linient in this manner. Also as soon as you've unlocked the Auction and Trade section from the store, you can buy players with higher stats which will help upgrade your group with cheap Madden nfl 20 coins. Go for the more cost effective ones however. Finally, you are able to test the Daily Challenges to never get behind in the race to max out in your MUT degree!