One common area of concern is the underarm...call it lunch lady arms, call it your angels wings...nobody likes when the bottom of their arm moves independently of your body. Triceps dips are a great exercise to target the back of that arm. It is a easy exercise that can be done at home, at the park, or at the gym.
Position your hands shoulder width apart on a secured bench. Move your feet out as far out in front of you as possible. Straighten out your arms and keep a little bend in your elbows in order to always keep tension on your triceps and off your elbow joints. Slowly lower your upper body down towards the floor and keep your elbows tucked into your sides. Once you reach the bottom of the movement, slowly press off with your hands and push yourself back up to the starting position with your triceps.
To increase difficulty put your feet up on another bench or place them on a physioball.