To achieve a major result in a sport discipline, psychological preparation must be very high on the priority list of an athlete. Tennis is a mentally very demanding sport, taking in consideration that the players are all by themselves on the court and the game is intermittent by breaks which gives the players a lot of time for thinking. The major goal of a sports psychologist is to help the tennis player to learn how to deal with his feelings and emotions to achieve the best possible on court results, which is done through various exercises and techniques. Some of the most important mental characteristics of tennis champions are analized in this paper work. Motivation, concentration, self-esteem and emotional control are all specially defined, as well as all the types, problems and theories of these mental characteristics when they are not on an optimal level. Further on, a list of exercises for increasing motivation, concentration, self-esteem and emotional control is shown and explained for on and off the tennis court. Rituals, breathing techniques, relaxation, meditation, yoga and similar are additionally added auxiliary techniques to improve the mental preparation of a tennis player. At the end of the work, there are explained procedures in the mental preparation of a tennis player, which are used before a match, at the time of a match and after a match. All of this is done to conclude in what state of mind does the tennis player have to be to put up his best possible performance.