put some stuff on the left, some other stuff on the right, and some other stuff on the top shelf.
very difficult to help you with a question like this on a message board. We don't know what you have been issued, how big your locker is, what your lab curricula are, what your favorite instruments are, etc.
I will offer a couple of general tips: eliminate as many boxes as possible. throw out as many old casts as you can. Get a small organizer with drawers for the small or unused stuff.