I like to make them up based on each dog's natural tendencies. I've found that to be a great way with both puppies and older dogs to begin a dialog. The play dead command, for example, or bang as I call it, is easy because when you walk upto many dogs they have a tendency to lie flat or flop over, which is exactly what you want them to do for the "bang" command! So it's both a natural behavior and a desired behavior, win/win!
With my pup I followed that up with a "freeze" command, which means head flat on the floor and no movement other than eyes until released.
My puppy also will back up if/when I approach her playfully....so, the backup command came into being, and she'll now back up any direction I point.
It's also helpful, as @Aly
pointed out in another thread to teach your puppy to accept/handle most medical procedures. So stand, paw (hand you their paw for drying or examination) on both sides, let you mess with their paws so you can clip nails as needed, lie flat for examination or x-rays. A gentle command, or easy, so they're careful with your fingers when taking treats, and a "booty call" which as you might expect involves gently wiping their bum with a damp rag...a prelude for a rectal thermometer if needed at the vet.
I also have taught a "bow" command, since she goes down in front so much naturally anyway, and a spin, though my pup seems to prefer one side better than the other so far. Speak, enough (to stop speaking lol), roll over, stop, wait (which for my dog is similar to stay except on wait they can move freely in the vicinity, whereas with stay I mean stay EXACTLY where I specify, in the position I specify (i.e.sit, down, etc.)
I guess the rest I could or would list have already been covered. Though after this you get into sport specific things, if you're into that...