Never sit on the table rails, it can cause them to fall off.

When playing at any level of competition, remember that the table and equipment "belong" to the shooter.  If your turn is over, you should move away from the table.  Standing around the table while your opponent is trying to shoot can be very distracting.  Also, since your turn is over, you won't need the chalk before your opponent needs it.  Leave it on the table.  It will be there for you when it's your turn again.

Every sport or recreation has its guidelines when it comes to etiquette, and billiards is no different. It helps to be familiar with these sometimes un-written rules when you try something new, and it makes it much easier and less stressful to know them ahead of time. Here are some of the basic dos and don'ts in the billiard room.

A. Respect your opponent and those around you.

1. No sharking!
   I figure this is a good place to start. Contrary to popular belief, sharking has no place in billiards. Sit or stand away from the table when your opponent is shooting. This one ought to be a no-brainer, but it's amazing how often I see a player minding their own business, trying to focus on a shot, only to have their opponent standing inches away, breathing down the shooter's neck. Some recreational sharks even go as far as placing themselves straight in line with the shot, "accidentally" twitching in the middle of the shooter's back stroke. It's not only impolite and rude, but moves like these-intentional or not- won't win you any popularity contests with the regulars in your local billiard room. So please. Have a seat.
2. Speak softly; control your language and temper.
   A billiard room is a place where men, women and children should be able to feel comfortable. So respect those around you by lowering your voice, mind your Ps and Qs and keep in mind how you would feel if the player on the neighboring table were to yell on the top of his or her lungs, just as you were lining up a game winner…
3. Mind your attire
   Before heading to the poolroom, picture yourself bending over the pool table and dress accordingly. We all have different levels of modesty and comfort and therefore there is no set rule of thumb I can recommend here. (But trust me ladies, I always do a mirror check before I head to a match.) Most important is to feel comfortable and free to focus on the game and have fun.
4. Respect your opponent before, during and after the match.
   See the points above, and always keep in mind the old saying - Treat and respect others the way you would want to be treated. And please. Unless someone asks for your input, don't coach others unless asked. This tidbit of advice will help save many marriages and friendships, believe me…
5. When shooting, always keep one foot on the floor.
   Getting up on the table is a no, no. This is not only etiquette, but a rule of the game. No exceptions.
6. Make it a point to be a gracious winner and a good loser.
   'Nough' said...

B. Respect the equipment

1. Keep food, drinks and cigarettes off the table.
   Not complying with this suggestion can end up having an even more dramatic conclusion than simply irritating your opponent. Replacing the cloth on the pool table is not cheap and it's amazing the damage a black Russian, a sticky soda or some barbecue sauce can do to the cloth. If at a billiard room, the proprietor will probably only give you one warning before you're faced with having to find a new place to play, while chances of being invited back to a homeowner's Christmas party after a major spill are slim.
2. Respect the property of the room owner, and play by the "house" rules.
   If there is a sign on the wall stating "No Jump or Masse' Shots allowed" then go with that. Even if you're a somewhat accomplished player, house rules rule…
3. No sitting on the table.
   Spend some time in a billiard room and you'll undoubtedly hear someone get yelled at from across the room to "get off the table!" This is an embarrassment that is easily avoidable. Unless a shot absolutely requires it, never sit on the edge of the table. The pool table has been meticulously leveled, ensuring that the ball travels the path you send it on, and excessive leaning on the rail will undo that work over time. In extreme cases, the slate seam can even crack!
4. Avoid powder at all cost.
   Another popular misconception is that hand powder is a staple in the billiard room. Not so. True, there are some places that will supply a talc cone, and talc is by far the lesser of two evils, but both get in the cloth and on the balls, thus affecting the game and the equipment. Try instead to use a glove. It may take some time to get used to, but if your hands are extremely sweaty, then it's worth the effort.
5. Keep clean!
   This is one of my personal pet peeves. Do not place the chalk upside down on the rail after chalking or you'll leave chalk residue on the rail that ends up getting everywhere. After chalking, place the chalk side up. This way, after a game you, your clothes and the table won't be covered in blue.
6. Leave everything the way you found it.
   Finally, keep in mind to replace everything just the way you found it. The rack and the mechanical bridge both have their place on the table and if you borrowed a "house cue," return it to where you found it and don't forget to bring the balls back to the counter!

That pretty much sums it up. Just keep in mind to show consideration for those around you in the billiard room, respect the equipment you play on and above all, have a good time!