The quickest way to get better is to find a play that you can score a touchdown on most of the time for practices. I used an outside run against a deep threat zone defense, then use your blocking to come out of each practice with 450.
Set difficulty to rookie
Stats increase more or less permanently based on your performance during GAMES as well, not just practice, so it'll settle you at a level at which you performed during the game, then adjust for practice.
Of course, look for an agent with PI access, and fight for every yard.
If you're on a team that doesn't run much, then just before the game, at the controller select screen, change "Off Playbook" to "Run Heavy" instead of whatever coach might be in there. That should get you some extra carries.
If line blocking is a problem, you can either fight through it or look to get traded.
Those are the standard ways of increasing stats, and they've worked for me, i've got a 99 OVR HB after 2.5 years.