Actually see what’s in that closet

If you’re lucky, you might have a walk in closet. If you do, I suggest a window in said walk-in. A window allows you to see everything in a clearer light. If you’re into matching colors and seeing your outfits better, light, of course helps.
If you have a smaller closet, or a walk-in that’s lacking light you can do the following:

Paint the closet interior with a bright white paint.

Use (or install) fluorescent lighting. If you use white bulbs it will show clothing and other objects in a more true to color form than say, yellow bulbs.

Go solar! Solar Sun Tunnels are really neat, use no electricity, and illuminate like you wouldn’t believe. Sun tunnels can be installed in most homes easily and quickly, and are perfect for lighting small areas like a closet.

Lose the sliding doors. If at all possible, go with a different style door. Sliding doors hide a lot of closet. In my opinion, even a nice hanging sheet that slides all the way over is a better choice.

If installing lights in your closet interior is out of the question, place a lamp with tilting head/s close by so you can adjust it to shine into your closet, where you need it. Use those white light bulbs too.