I wasn’t aware of the “rule of 600″ thing, where you divide your lens’s focal length into 600 to determine the maximum exposure length. Good to know! It helps to have a high-ISO capable camera as well, but it’s not necessary — I’ve gotten perfectly clear stars with my old Rebel XSi.
I’ll be heading up into the country in a month or so, and will definitely put some of these tips into practice. If you’ve got a tripod and can spend an hour or two outside where you are, you should try it as well.