[eru]

I was assuming you were talking about a standing shoulder press. (In general, standing is better than sitting for your exercises. If nothing else it uses more of your body and mind to stay balanced.)

If you are standing, you've got no choice but to keep your centre of gravity over your feet. Once the weight is heavy enough, the bar will largely determine your centre of gravity.

If you are sitting, then, yes, you have the option of doing an incline press. That's where you lean back a bit. A mix between a shoulder press and a bench press.