I’m pretty sure similar tips have been mentioned before, but here’s a little different angle.

Most bottles of paint do not contain a ball (as spray-can paints do) to help mix the paint. So, I bought a “bucket of beads” at Hobby Lobby for $11.99 (actually, less because I had a coupon), and now I have a lifetime supply of paint agitators. The beads are glass (no worries about rust) and come in three sizes: 4mm, 6mm, and 8mm. Add one to any kind of paint, seal the cap, and shake well to make sure your pigment and carrier are thoroughly mixed for optimum paint performance. 

Tip submitted by:
Gerald BakerEl Paso, Texas