1. MENTAL QUICKNESS- You have to be willing and able to adapt to what your opponent is doing. I can't tell you how many people i have played that do something over and over again even though I have established that I will shut it down. Don't be too fast to call off your gameplan, but there is a time to remove certain parts of your gameplan if it is obviously not working. I am a very firm believer that madden is a mental game as much as anything. If you outhink your opponent, you will usually be in a good position to win.
2. Stick Skill- In my opinion stick skill is extremely overated. That being said, you need amazing stick skill to become a truly elite madden player. But stick skill (especially on defense) will only help if you have my #1 point (mental quickness) down and you have the right play called and you are in the right spot to use your stick skill.
3. Labbing- I know that the temptation is there to play random people online and try to improve your rank. As most of you know, online rank means very little. Instead of playing random bums online, you need to be disciplined and practice the weaknesses in your game with people you know can help you, challenge you, and expliot your weaknesses. I believe that truly elite players are set apart from others because they lab more than they play.
All three of these factors are intertwined in ways. Labbing inproves stick skill, mental quickness makes your stick skill look better, Labbing improves your mental quickness and your ability to adapt, etc.
I think that the most important factor in becoming good in madden year in and year out is mental quickness. If you arent able to think, you will never do well in madden even if you lab all the time and have amazing stick skill. Everything is based on your mental quickness in my opinion.