Your bedroom should be a sanctuary, a place of rest and relaxation. Your nightstand should reflect that and not be so messy and disorganized that you can't find things or that you can't calm down cause you are reflecting on the mess instead of relaxing.
Ideally, the top of your nightstand should be large enough to hold a book, a light, and an alarm clock (and a vase and eyeglasses, if you require them). The nightstand should also have a drawer to conceal items that would detract from your bedroom decor, such as prescription medicines, the television remote, and a small flashlight. If you have a number of medications or other items you use while in bed, consider a nightstand with multiple drawers. A shelf underneath is useful for holding magazines and books to be read. If an item is not used while you are in bed, it doesn't belong anywhere on or in the nightstand.
Hopefully this helps make your room an oasis and a restful, relaxing night! That's what works for me!