One of the fun aspects of tennis is out-thinking your opponent.  On the serve, having a plan in mind is a pre-requisite to its execution.  The following suggestions will help stimulate your thinking.

   1. Make first serves. Doing so will reduce the pressure on yourself and apply it to the receiver. It's human nature to seek the easy way out of the point (i.e. toss the ball up and hope for an ace). The risk-taker bucks the odds, then suffers the consequences. The alternative is to compromise -- to make a well-placed serve that is difficult to return well.
  2. Develop the second serve. At higher levels of play an aggressive second serve is essential. More spin, pace and depth keeps the receiver in the backcourt. Keep in mind that the tradeoff for more double-faults is missed and short returns.
   3. Make the receiver play the ball as he moves laterally, not forward.
   4. Apply extra pace to the poorly produced stroke. Know which stroke is more penetrable; use the flat serve to break it down.
   5. Use the element of surprise as a weapon. Mix up placement with both slice and spin serves. On the deuce court, if you always go wide with slice and down-the-center with spin, your opponent will be able to read the toss. 
   6. On the deuce court, make the receiver hit a backhand from the sideline; on the ad court, make him hit a forehand. By pinning him in the corner, a weak return gives you an open court.
   7. By serving down-the-middle, you increase the likelihood that the return will come back down-the-middle, which improves your position to play a forehand or a volley.
   8. Serving frequently to the body on the deuce court sets up the wide slice serve.  Looking to hit a forehand, the receiver may back up, opening the wide serve.
   9. Serving wide to the forehand on the deuce court sets up the slice serve to the body, or the flat or spin serve down-the-center.
   10.  Kicking the second (or first) serve to the backhand may set up an effective kick serve to the forehand. (He sees the toss, takes a first step to the backhand, opening up an off-balance forehand return.)
   11.  Avoid kick serves to the backhand that land short. (On the deuce court these are potentially dangerous when the receiver has time to run around his backhand and smack the return crosscourt.)
   12. Go into the body frequently.  Keep in mind that it's difficult to move the body away from the ball, and that the racquet doesn't work effectively when the stroke is cramped.
   13.  Don't always allow a receiver's strength to influence your placement.  Generally you must go to a strength first to expose the weakness. (The same player who enjoys running around his backhand on the deuce court may not be so successful when moving to his right.)
   14. Cut down on netted mistakes; they're contrary to your strategy of placing the ball deep. Doing so may mean that:
     a. You're not reaching high enough. (Fatigue?)
     b. You're dropping your head prematurely. (Are you watching the ball at contact?)
     c. You're tossing too far forward.
     d. You're tossing the ball too low. (Try keeping your tossing hand up a second longer.)
 

Playing the Points  (Suggestions--do what works for you.)

First point: Make it. Give yourself the biggest margin-for-error, by going to the body. For effect and consistency, use some spin. 
   In matches it helps to hold onto a few beliefs. Example: The statistical chances of winning the game, after winning the first point, are high. The chances of winning the point, after making the first serve, are similarly high.
 

Second point (regardless of score): Go to opponent's strength. If he favors forehand hit it there, flat or a bit of slice. Consider that you must often go to the strength to get at a weakness.

Third point (15-all, 30-love, love-30):  Go to the body. Believe that this point has the greatest value. (At 15-all it tips the balance; at 30-love it gives a commanding lead; at love-30 it tells opponent you're not conceding game, and that with one more point you've evened the score, and gained the momentum.)
 

Fourth point (40-love, love-40): Take a chance with the first serve. Anticipate that your opponent is thinking along the same lines. 15-30: If you lost the preceding point, improve the percentages by increasing your margin-for-error (slice to forehand, into body); if you won preceding point go with your intuition. 30-15:  Think aggressively.
 

Deuce:  Mix it up.

Ad:  Generally, when ahead in the score, play boldly (or with cleverness); when down in the score, improve margin-for-error.

Combining Serve and Groundstroke/Volley
   #1  Slice wide, follow with a groundstroke to the open court.
   #2  Hard and flat, or slice, to forehand -- to force short ball. (Extra pace to forehand, hoping for a late hit.)
   #3  Slice or flat to body, forcing receiver to play a backhand (hit from sideline), opening court for groundstroke or volley.  The idea is to pin him on the sideline.
   #4  Flat, spin or slice to T, eliminating angle of return -- to produce first volley to backhand, or inside-out forehand, or to pick on his forehand. 

Excerpted from Watch the Ball, Bend Your Knees!