My father used to swear prolifically on the court. It seemed to work for him.
Tennis is a mental game. If your physical game is at least in the same ballpark as your opponent's, it's up to you mentally to know you can beat him or her. Convince yourself of it.
One of the quickest ways to obtain good form is to catch your racket on the follow-through. When hitting a one-handed forehand, racket-back, point your empty hand towards where you want the ball to go, step into the ball, swing at waist level, connect when the ball is just in front of you, and follow-through by catching the racket & your dominant hand with your free hand. Continue with both hands until the racket is back above your shoulder.
Every swing should be roughly the same. That is, a forehand down low should have the same swing as a forehand up high. What will change is the bend of your knees, or the positioning of your feet.
Big serves are overrated. If you're a little guy, learn to use your opponents' power to make your strokes more powerful.
This is an obvious one but you'd be surprised how many people don't do it. Find your opponent's weakest shot (ex. insideout backhand, ex 2. down-the-line forehand) as early as possible in the match & make it a point to hit the ball there as much as possible. Also note that his or her weakest stroke might change as the match progresses & fatigue sets in.
:: More musings ::
In doubles, make sure to communicate with your partner after every point, even if it's just a nod or a tap of the racket. A line of communication is one of your most important tools.
Whenever you're down love - 40 play every shot as a winner. Take risks; your opponent will be playing conservatively.
Don't ever let the sun, external noise, or the attitude of your opponent get in the way of your game. If it does, you only have yourself to blame.
Tennis may be a rich man's game, but don't let it intimidate you. On the tennis court, at least you have far more opportunities to beat the rich man in a fair & square game, right?
Always hit synthetic gut.
Go to the net. Even if the net is not your game.
Get the correct, natural tennis stroke down. Even if it takes hitting that stroke over & over again for hours & days. Once you've got that natural, correct stroke, it's hard to forget it & picking up where you left off after a vacation from tennis is a lot easier.
Play to play & improve your game, not to win. Otherwise, you're just going to lose interest in the game. Well, if you're anything like me, that is.