So apparently I've forgotten a lot about this game. I didn't even remember you could customize your own plays. The play that always worked best for me is below. It's a custom play I set up back when I was really into this game. I've drawn in the routes for the receivers so you can set yours up the same way. After you snap the ball, the fullback ("C" on the diagram) will run to the right and cut downfield. Nobody ever covers him, so this will set you up for some easy touchdowns.
On defense, it's not too hard to get interceptions during passing plays. I just try to get a defender in the area of the pass and mash the B button, and every now and then I come up with an interception.