When someone is trying to do too many things or working too hard, you can say “Don’t bite off more than you can chew!” as a friendly suggestion to not work too hard as you might make a mistake in your work if you do.

It means “don’t work too hard (that you make a mistake).” It’s a very casual phrase, so use it in the appropriate setting!

Example:

A: I just got hired at a third part time job. I think I might be working too much, but I really need the money!

B: You’ll wear yourself out working that much! Don’t bite off more than you can chew.