Ready For Play
A smart tennis rule of thumb is when you're ready to play, put racket covers, ball cans, jackets etc., out of everyone's way.
Tennis Code and Rules
Tennis has its official tennis rules, then it has The Code of Tennis, the unofficial rules of good tennis sportsmanship. Any serious player should take the time to read both. Players who don't understand the rules, or worse, The Code, are more likely to experience a gradually shrinking pool of opponents.
New Balls
This is more of an etiquette than a tennis rule. Offer to bring new balls or organize a system to decide who brings the balls.
The Code
Colonel Nic Powell, the author of "The Code", is credited with simplifying tennis rules. His document is succinct and to the point. To sum it up in a sentence, play tennis using the "Golden Rule" as your best guideline.
What is the Golden Rule
Your mom and dad taught you the Golden Rule, didn't they? Why? Because it condenses appropriate behavior into one sentence. "Treat others the way you wish to be treated." The same holds true for an opponent and a questionable call. There's nothing wrong with challenging the call, but once a call is made, accept it, and proceed with the next point. Call it the golden rule of tennis.
Attack the Net!
Do you like net play? Then, the tennis rule of thumb is you need to master the serve and volley! Serve to your partner and then get to the service line before the ball is returned. Hit the ball out of the air, and play out the point. Remember, if you come to the net and the ball is high, it's offense for you. If it's around or below the net, it's defense for you!
Talking
The unspoken rule of tennis for spectataors on tennis courts is to be polite. Talk quietly when standing near tennis courts that are in use. Never walk behind a court when a point is still in play. Wait until the point is over and then cross as fast as possible.
Serve
It's not an official tennis rule, though , to see who serves first people usually spin a racket or toss a coin. If you win the toss, the choice is yours. You may serve first, or you may choose to receive first or to pick which end of the court you want to start playing on. As a third choice you may make your opponent choose first.
Line calls
In doubles, a tennis game rule of thumb is you should not call balls wide when they land near the far sideline, unless the call is obvious and your partner was somehow hindered from seeing the ball land. If you are the receiver, and your partner is on or near the service line at the start of a point, your partner has the best view of whether a serve is in or long. You can make a call if he doesn't, but always defer to his judgment. (You generally shouldn't disagree with your partner's calls anyway.)
Baseline to Baseline
The key to baseline rallies is height. Visualize the net as being higher than it is, and your balls will clear the net, and will land deeper. Avoid hitting balls around the net area. Though, if you do hit the net during play, but the ball still goes to the other side the tennis rules state that the ball is still good. As long as it didn't go out of bounds.
Questioning Calls
Whenever you hit a ball close to the line and your opponent calls it out walk up to the net and say something like "Are you sure about that?". Stare at the place where the ball hit the court and then, as you shake your head in disbelief, slowly walk back to the baseline. This should be done whenever there is an opportunity for it. The official tennis rules state that if there is a referee available you have the right to call him/her out and demand that s/he assigns a line judge to your court. The purpose of doing this is to make your opponent think twice before s/he makes a call. Unexperienced players often become unsure of their own calls at which point they are easily manipulated.