1) Leave all of the political talk at home. Too many people treat a gun store like a barber shop and feel the need to go on rants about the federal government, ATF, the latest court ruling in your jurisdiction, etc. I've had this experience waiting for some a-hole to finish up with the clerk after discussing the finer points of Heller . Just buy what you want and get the hell out.
2) Refrain from engaging in useless 9mm vs .45 debates with the guy at the counter in an attempt to impress him/her and the people around you with your 'knowledge'. Unless you're a total n00b and really don't know the difference then that's fine.
The left and other high and mighty folks have been telling conservatives for years we have to keep our mouths shut. I have a solution for this. One of these days...