Keep your back straight throughout the movement. Dont let it arc too much when pressing the weight.
Use slow and controlled movement, both when pressing and when lowering the weight.
Use a full range of motion by lowering the dumbbells as far as possible, and raising all the way up without locking your elbows out at the top of the movement.
Keep your core tight throughout the movement. Doing this will ensure stability and benefit your abdominal muscles and core strength greatly.
Instructions
Choose a pair of dumbbells and sit down on the center of an exercise ball and tighten your core.
Raise the dumbbells above your head and twist so that your palms are facing forward. Your back should be straight and your feet firmly planted on the floor for stability. This is the starting position for the exercise.
Keeping your eyes facing forwards, slowly lower the dumbbells to the sides of your shoulders.
Once they are around shoulder height, contract the shoulder muscles and raise the dumbbells back to the starting position.
Do not pause at the top of the movement, and immediately begin lowering the dumbbells back down for the next rep.