Here are some more idioms with "keep" to keep you on your toes. (Do you remember that one from the last post? If not, look back and read the definition and examples again.)
1.) Keep (Someone's) Cool
This means to stay calm; don't get angry when you are in a situation that is frustrating. For example, you might say to a parent who is about to become very angry with his or her child, "Keep your cool! Don't get too upset."
2.) Keep Track Of (Something)
This means to be organized, not to lose something. For example, you might tell your child, "You must keep track of your homework. If you lose it, you will not get a good grade from your teacher."
3.) Keep a Straight Face
This means that your face does not express the fact that inside, you want to laugh. You do not smile or laugh. Continuing with the children-themed examples, if your child does something really silly that he or she should not do, you must keep a straight face so that he or she doesn't think you think it's funny.