I diagnosed that my biggest weakness was in my defense. While I'm able generally to move the ball down the field with ease against computers I was relying on my intuition to select defensive positions - and even though you could just around get away with this when you're playing against artificial intelligence, it's impossible to be able to do that against an online opponent, who will be able to see what you're doing and then make changes to attack it.
My thought process was that If I understand my defense, I'll know it's strengths and weak points. This means when it comes time to play offense, I'll know how to exploit my opponent. So I started working on trying to garner an understanding of the patterns; I learned how to stack the box into a 3-4 or 4-3 patterns in the event of a run and to work in Nickel or Dime when the opponent is likely to throw the ball, for instance, on a second or third down.
I found success in Man coverage generally, though I began to employ Zone in situations where I was content to offer my opponent a little field. If, for instance, I'm leading and there are a couple minutes remaining, I'm okay with letting my opponent play in front of me. I'll use a Cover-3 Deep configuration to give my opponent some grass, knowing that I'm unlikely to give up the big shot. You can still be in the way if I do this - good players will play from the sidelines for instance - however, I'm generally having success.