RE: Maintaining, not growing
I started with 3 sets of 10 of military press (machine), but then went to using db's as they give your rotator muscles a bit of a work too. I now do 4 sets of 10 with db's, 3 x 10 lateral raises, and a couple of sets each of front and bent over raises.
Recently I've just started doing crossed over lateral raises on the cable machine, works your delts through 135 degrees or more- I don't know what the hell it's called, and it's hard to describe but it works a treat!
In a nutshell though, I'd go for 3 or 4 sets of each of your chosen exercsies, 8-10 reps per set, down to 6 reps for the last set if your're going HEAVY. Keep at it, with a good routine, diet and sleep they WILL grow!