It can be tough to avoid flat spots when sanding a curved object like shelf bracket, but if you wrap the sandpaper around a tennis ball, it's much easier. The rounded shape of the ball helps you get just the right angle you need. Image from madeline.gannon.
Of course, you can get the same effect by using a rotary tool with sanding attachments, but if you don't do projects like this (furniture, shelf brackets, curved box tops) often, the tennis ball and sandpaper technique is much cheaper.
10 Unusual Uses for Tennis Balls [Instructables]
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