Gym Etiquette the Basics…

1. Smell normal - nobody wants to workout beside someone that smells like they have not showered in a few days.
2. Wear clean clothes and shoes -  clean clothes goes hand in hand with odor.  Don't come in the gym wearing shoes that are tracking dirt all over the place.
3. Re-Rack Weights - Don't be lazy put up what you used.
4. Clean Equipment - After your done especially on cardio wipe down your machine.  On weight benches and machines etc put a towel down.
5. Talking - If your going to talk make it quick and during rest period in between sets. Otherwise your holding up the piece of equipment.  I personally do not like to talk at all during my workouts.  I'm their for a purpose and I don't want to lose my focus.
6. Leave your ego at the door! if you can't lift it correctly don't lift it at all!

Feel free to add any others that I did not list in the comments.