This is absolutely, 100% a "well, duh" post, but it has long been on my to-do list and after finally getting it setup, I thought I'd share.
Apartment living can force you to improvise when it comes to how you use a small space. If you have limited closet space, you're definitely going to have to take a single area and give it multiple uses. One space that is common in homes, but nonexistent in apartments is the garage or workspace. Sure you probably have a super that can come and take care of things, but everyone still should have basic tools for day to day issues/projects.
Instead of pulling out an overstuffed, messy toolbox every few days, I decided to hang my tools on one side of my coat closet via mounted pegboard. This will help keep things organized and conveniently located. And it is oh nice since having my closet floor vacant of the ugly, always open, disaster of a toolbox.
It can also be useful for vertical office supply storage, arts & crafts, cords, and much more.
Project cost: ~$15 in pegboard, hooks, and hardware.