It is really hard to find a balance between working too hard and working not enough. If you work too hard, usually during test seasons, you wear yourself out. And as soon as the tests are done, you crash and don't do work for a weekend or so. This causes work to pile up causing you to go back to overworking yourself. I'm going to share a method I'm using to avoid overwhelming myself.
The first thing I do is make sure I don't let any day pass with me doing no work at all because even if you do one of four assignments one day, its one less assignment you have to do later. Keep yourself working, slowly and surely.
I make sure to write down everything I have to accomplish in a day in my planner and make sure that I look it over throughout the day. I divide my work by doing the work for an easy class then a hard class and then another easy class. This keeps my brain from overworking itself one the hard assignments while still getting a lot of work done.
I also highly recommend not leaving studying for the last minute. I know, everyone tells you this but seriously, last minute studying is never a good idea, not for your health, nor your grades. To truly learn, absorb, and retain info, you need to expose yourself to it multiple times. My game plan is to take notes in class, then rewatch the lecture online because my hard classes have their lectures recorded and put online. I then will do practice problems or memorize the information I need to. It sounds pretty easy but it takes a lot of will power to keep on track with my work. I hate going off track because the more that work piles up, the less motivated I am to do it.
If you really want to succeed in your classes, make sure you are putting the required amount of effort into the class.
Hard work always pays off so don't give up!