You can find a number of good arm stretches; which one you choose depends on which part of your arm you want to stretch. A good overall upper body stretch–one that stretches your back and shoulder muscles as well as your arms–is something I call the Yawn Stretch.
Either lie on your back or sit on the floor, and raise your arms up. Keeping your elbows slightly bent and shoulders relaxed, lift up nice and tall. Now lean to the left as you pull your left arm down to your shoulder and stretch your right arm up and over to the left even more. You’ll feel this stretch up your entire side to your fingertips. Hold the stretch for between 10 to 60 seconds, then repeat on the other side.
To stretch your biceps (the muscles at the front of your upper arm), extend your right arm out at shoulder height with your palm facing up. Place the palm of your left hand over your right fingers and gently press down. Again, hold for 10- 60 seconds, then repeat with your left.
To stretch your triceps (the back of your upper arm), raise your right arm straight overhead, and then bend your elbow back so that your palm is resting lightly against the top of your shoulder. Place your left hand just underneath your elbow and gently press back. Then switch hands.