Some of the Shoulder presses are poorly made and you cannot help it. I would find another way to do them if you have a poor bench like that. The one at my current gym, sucks. It wobbles and makes you lean back too far. I just use the Smith machine.
Some people like to use a close grip on the bar.
I don t, like close grips, they tend to work the triceps too much. I recommend the same grip that you use for the bench press. If you are doing these from the front, just lower the weight to the collar bone and not any lower than that. If you are doing these from the back, then lower the weight to the base of the neck and not any lower than that. So many people lower the weight too low, on these and create injuries.