The Arnold Press is one of my favorite exercises for the shoulders. I prefer to do them without back support. Stabilise your body and shoulders through the whole range of movement. Don’t cheat, control the movement up and down using a tempo of 30X0.
http://www.youtube.com/watch?v=vcqvpRYUVyw
Suggested Sets and Reps: 3 to 4 sets and anywhere from 6 to 15 reps depending on training phase and shoulder strength
PS. This is a great exercise to use with older clients