Last month I mentioned that the two best exercises to do to get your arms ready for beach season are dips (for triceps)and pushups. Pushups on the floor (on your toes) may seem very challenging but a great way to work up to that is to do pushups on the ball.
To do pushups on the ball: -Start kneeling behind the ball. -Engage the abs and roll out onto the ball (face down) until your knees are on top of the ball. -Walk your arms out so that your hands are wider than your shoulders. (Hands should be in line with shoulders) -Bend the elbows lowering your chest towards the floor. -Perform 10-15 of these. - Remember not to flop over when you are done. It is important to get off of the ball the same way that you got on it. Walk your hands back until you are kneeling behind the ball.
As you improve you can walk your body further out on the ball until your toes are on the ball. (see picture below)