This one is not only useful, but it looks cool as well. Start by placing your fingertips of each hand onto one another. It should look like you're holding an invisible ball in your hands, or like a spider walking on a mirror. Apply a little pressure until the fingers start to bend outward together. Keep applying pressure and gently press down until your fingers are straight but your palms are not touching. Then slowly lift back to the starting position. Do this as many times as you feel like. This exercise is great for strengthening all of the muscles in the fingers and also improving dexterity in both of the hands simultaneously.