One of the best shoulder exercises I know is a form of the overhead press done with a single dumbbell, one arm at a time.
This allows you to press a little heavier weight than is normal and is definitely a help if you have weaker shoulders. When you lift this way, you can keep what it called "stacking" in place, with your wrists stacked over your elbow, which in turn is stacked over your shoulder, thus keeping your arm closer to your center of gravity.
My son in law also suggested I try the Arnold Press, which looks like this. Eager to give it a go the next time I'm in the gym.
Have a wonderful day everyone!