This means to stay in control, and not get behind or let your work pile up. Ex: I’ve got so much work on at the moment that it’s difficult to stay on top of it

This phrase comes from the sports field. When you are on the ball, you have to be alert and sure not to make any mistakes. Ex: Sam’s really on the ball.

This means to think of a solution that is different to what is normally done or to think of an unusual, creative solution to a problem.