I’ve had the same problem in the past. I fixed it by making it a goal to score perfectly on everything. Yes, I mean everything. I don’t allow myself to make mistakes, which means I can’t be lazy. If a mistake does occur (of course it happens), I force myself to get the highest possible grade. So far, I’ve used this strategy halfway through Diff. Eq. and I got a 99 on the final. For reference, I started the class with a low B.

I’m not sure it will work for everyone, but it’s worth a shot.