Tips for balancing a part time job and a full time student?

I started this job because I didn’t want to have another unproductive summer and I love it! I feel like I’m gaining alot of experience and I enjoy being a busy person. But now that school has started I want to make sure that I can achieve my goal of a 3.65 this year without work interfering.

I’m scheduled to work about 20 hours a week now and am taking 15 units at a university. So far I don’t feel like I’m neglecting any of my courses (which is my main priority).

How do I make sure that I won’t slip up with school? I’d rather not trial and error this.