How to balance part-time work with full-time studies?

I'm a third-year student working 20 hours/week to support myself. Finding it increasingly difficult to maintain good grades while working. Current Schedule: Classes: 9 AM - 3 PM (Mon-Fri) Work: 4 PM - 8 PM (Mon-Thu), 10 AM - 6 PM (Sat) Study time: Limited to evenings and Sundays Any tips from students who've successfully managed this balance?