Here is an example of 17mm on a 50D, shot in a pretty dark sky. One thing you want to do is have some type of identifier in the scene, whether it's a easily discernible constellation, some type of horizon subjects like trees, or any other subject (besides the stars) that can aid in showing what the scene is. To most people a shot of the night sky won't look like anything except for a bunch of white dots on a dark background. If there's something that's apparent it makes it easier for people to understand and enjoy the photo.IMAGE LINK: http://www.flickr.com/photos/katodog/8622670074/ April 04 001
In this shot there are several things, one is the trees that aid in defining a "horizon". The other things are the constellation Orion, which is almost centered in the shot. Jupiter off to the right a bit, and the Pleiades to the far right. Now of course these things can be virtually unknown and unidentifiable to most people, but what they do is show some areas of definition; you see "structure" in certain areas, and it breaks up what could be a potentially boring photo. It also allows me to show the photo and say "this is a shot of Orion, Jupiter, and the Pleiades", which will make people think and it'll give them an idea of what they're looking at.
by Ed Durbin (Katodog)
, on Flickr
The other thing you want to do is practice. Practice, practice, practice. It takes a lot of practice, knowledge of the night sky, and patience, to be able to know the best way to shoot the night sky and the stuff that's in it. The shot I posted is a single exposure, 15 seconds, ISO1600, f/2.8. There's no need to stop-down aperture because the camera sees the night sky as a flat field, so you won't see distortion unless you have a defined horizon and foreground. So you can shoot wide-open, and as long as your focus is good you should be able to get a decent shot. You just have to have something to look at besides a bunch of white dots across a dark background.
Take the time to learn a bit about what's up in the sky, it'll help you pick a good area to shoot at so there's something in the shot. Also, try using a program like Stellarium or Starry Night to teach you what to look for, what the different constellations and star clusters and whatnot look like. If you can take a picture, then say "Here's a picture of Saturn that I shot last night..." it'll at least give people an idea of what they're looking at, they won't think it's just a blank background with random stars.
Anyway, I could ramble all day about the subject, but the best advice is to add something to the photo, foreground subjects, horizon, whatever, so people can at least say "oh, that's a picture of...". Practice camera settings, try different lenses, practice makes perfect. Or close enough anyway.