A'ight, you can take screenshots by typing "screenshot". Or more preferrably, typing "bind 1 screenshot" and pressing 1 to take it so the console isn't in the way.
Anywho. As for making good special stages. Just look at SRB2's stages. They're kind of like the ones in Sonic 3 but with rings. Also, there should be platforms, but make sure they're not too easy but not to hard.