Pressure drills create a competitive environment where players are challenged technically, tactically, psychologically, and physically.

Whether it is the number of serves made out of 20 attempts or the score between two players in a crosscourt forehand game, pressure drills involve some sort of counting. Pressure can only be created in a game environment where score is kept.
Are segments of points or situations that occur in match play.
Pressure drills must be as realistic as possible. A drill has maximum value when it simulates an actual match situation. Some drill sequences may involve only a few shots. For example, a four-shot sequence might be serve, return, groundstroke, and groundstroke. This drill emphasizes the first four shots of a point.
Use simple scoring that is easy to grasp.
The object is for the players to focus on playing rather than performing mental gymnastics when trying to keep score. You’ll be amazed at the scoring possibilities you’ll come up with. Believe me, I have learned the hard way on numerous occasions. Keep it simple!

Involve competition against teammates or a standard.
Pressure drills are competitive. Most pressure drills involve competition between teammates, but in some drills, the players are competing against a standard (when serving, for instance).
Start with a serve or a feed from a player.
If possible, pressure drills start with a serve; otherwise players feed the ball to start the point situation. There are only a few pressure drills in which coaches feed to start the point.
Are timed, have a certain number of repetitions, or end when a desired score is achieved.
Although tennis is not a timed sport, most pressure drills are timed. Timing drills not only maximizes court time, because all drills end at the same time, but it actually creates numerous pressure situations, because games are frequently tied and single points decide winning and losing. Tiebreaker scoring is often used in pressure drills by playing to 7 or even 11. Also, a certain number of repetitions might be stipulated, such as serving 20 serves, 10 to the deuce court and 10 to the ad court.
Have a consequence.
Players either win or lose a pressure drill. Winners move up a court and losers move down a court. I have known coaches in other sports where pressure training is used who have the players choose a physical consequence for the losers to perform after a drill (push-ups, sit-ups, or line drills, for example).
Have recordable results.
After each pressure drill, a score and result can be recorded. For example, players who win a drill or achieve a desired standard receive a "+" (plus) and players who lose a drill or fail to achieve a desired standard receive a "-" (minus). In addition, the score can be recorded. For example, if your standard for a "+" is making 17 or more serves out of 20, it is helpful to record the score to know how close the player comes to the standard. There is a big difference between making 8 of 20 and making 16 of 20 serves, even though both are recorded as a minus.
Have restrictions (including no restrictions) and stipulations.
Making players play within defined parameters teaches discipline, exercises their will, and forces them to problem-solve. For example, not being allowed to hit down the line in a crosscourt forehand drill promotes a point-building mentality and changes the focus from attacking the open court to patience. How will the player solve the problem of not being allowed to apply pressure down the line? Also, good opponents in match play can take away favorite preferences and options. Again, learning to be comfortable with the uncomfortable and unpredictable will pay tremendous dividends.
Have a tactical focus - every shot has a purpose.
The big three (Directionals, court position, and shot selection) provide a tactical focus for every shot. Forehands are no longer just forehands but might be point-building outside forehands or pressuring inside forehands. Depending on the shot, the player adopts a specific tactical aim and mind-set. Given this tactical focus, drills have to be realistic or segments of points.
Promote proper tennis behavior and etiquette.
Because pressure drills are games won or lost, they evoke typical responses to winning and losing - some good, some bad. When pressure training, practice becomes a great opportunity to work on proper behavior and etiquette. Players will experience the same emotions they experience in match play, from anger to frustration to apathy to elation. There is no better preparation for good match behavior than having developed proper responses to difficult situations beforehand.
Require decision making and problem solving.
Because pressure drills are segments of points that occur in a tactical framework, players must strategize and problem-solve each shot. Important factors affecting players’ decisions are who their opponent is and their style of play and the drill restrictions. For example, it makes no sense to try to overpower an opponent in a crosscourt groundstroke drill. Each player knows where the ball is being hit, and very little open court is available in which to hit penetrating shots. In this case, it should be obvious that the crosscourt forehand game is a game of patience and errors rather than winners. As you will find, each pressure drill is clearly a problem to be solved.