Spread your fingers apart really wide, as if you are trying to palm a basketball. Now tap each finger to your thumb one at a time. Starting with your little finger or index finger, go all the way down and all the way back. Every time you tap a finger, come back to a full extension.
Use an eagle catcher. An eagle catcher is a tool used by martial artists to strengthen their grip, which is beneficial when they are performing chokes and throwing opponents to the ground. This tool works the fingers and can strengthen and help tone them (see References).
Become proficient at typing. Typing is a good exercise for developing coordination and strength in your fingers. Practice typing on a conventional typewriter or a computer.
Open and close your palm. This exercise can be done anywhere, at any time of day. Clench your fist as tight as you can. Then open your hand and spread your fingers apart as wide as you can. Alternate back and forth.
Perform some push-ups. Come into a plank position with your hands directly under your shoulders and your arms straight. Spread your fingers wide apart and come up onto your fingertips. Lower yourself down by bending your elbows, then push yourself back up.