Absolute biggest thing, as mentioned is safety. I'm sure the person taking you will mention proper firearms etiquette, whether you are indoors or at an outdoor range. Biggest things are: Always keep the firearm pointed in a safe direction which would be down range when at the line. Or, pointed downward when approaching the shooting line. Even while not in use/unloaded it's good practice to keep your firearms pointed down range. If you have a failure to fire/eject, drop the mag and rack the slide/pull charging handle. If the round ejects/cycles properly it's safe to insert the mag and continue. If you are unable to free the round from the chamber, ask for assistance from an experienced shooter. Wear good ear protection. It's also common courtesy to make sure anyone else in the immediate area also has ear protection on before shooting. This one pertains more to outdoor shooting. If you want to go out and change your targets. Be sure everybody shooting is aware you intend to change targets. Typically folks will finish off their mags and then wait for you to proceed. It's also advised to not handle firearms, or load mags while folks are downrange. Be safe and have fun!