I usually make use of concepts and experimental results I encountered in psychology courses. Here are a few that might interest you:
1. The Atkinson-Schiffrin model of memory shows how multi-tasking is detrimental to executing tasks each task by introducing the idea of a limited ability to pay attention (specifically, this has to do with the availability of blocs of information in short term memory), as well as how learning occurs (by making blocs of information larger);
2. The concept of a zone of proximal development that lies between acquired skills and skills that are out of reach explicits why you need a specific level of difficulty to learn. Developmental psychology also insists on tying challenges with the appropriate ressources to meet them and learn. Applying those ideas tells you exactly what you need to improve at anything. Also, as improvement is including more tasks within the set of acquired skills, it means we have to increase the difficulty of challenges to match increasing skills;
3. Piaget's concepts of assimilation and accomodation breaks down learning in terms of width and depth. Assimilation works through repetition (as you iteratively execute a task, it becomes part of you) and, accomodation, through the confrontation of assimilated skills with new circumstances (if you learnt that pulling doors open them and run across a sliding door, by jerking it around you will eventually learn that there exists many doors). So we have width and depth, introducing new skills and adding nuances -- each aspect imply, as you might guess, different challenges;
4. We can think of speech as an indicator of thought. As such, requesting that a person shouts out loud decisions gives insight about when those decisions are made and, sometimes, also about the presence of hesitation in the process. That can be used to devise drills to improve decision making;
5. In communication psychology, there is a distinction between trigger events and events to which we react -- which need not be real --, as well as the possibility to become aware or not of this reaction. On a tennis court, people often express emotions following successes and failures, but many of those events only trigger reactions that have to do with something else. As for awareness, everyone probably encountered or experience a moment of anger where the person is very red and screams "I am not angry!" If you refer to 4 and 3, you can understand how giving precise names to your feelings may help you become more aware of them;
6. We can also think about the intensity of emotions. As emotions are more intense, so are the reactions -- but the twist is that not all people react the same way. Some people need to experience considerably more intense stimulations to react -- those people tend to enjoy spicy food, put a lot of condiments on their hot dogs, burgers, sandwhiches, etc. Other will be very responsive to anything. For instance, any kind of surprise can severly startle them. For one person, a small tear can be like someone else crying a river -- keep that in mind when reading your opponent or yourself;
7. It is impossible to not express emotions. You cannot silence your body, but you can displace the expression from one place to another. This does suggest you should find subtle ways to express frustration or joy during a match to avoid giving too many clues to your opponent at the wrong time, but it also comes with a long term message as well. If you are clever, 7 and 5 reminds you of some relationship problems: you know, people who don't talk and end up breaking up after a huge fight over a very silly thing. A similar thing could happen on the court;
8. Emotions can distract you in a way that 1 explicits -- i.e., expressing emotions is doing something, just like paying attention to them. As such, getting very angry or very anxious during a point will impair your ability to execute tennis related tasks.
There are others. If you are interested in acquiring a finer understanding of yourself and of your reactions, I would suggest that you try to find a simple presentation of the 8 stages of socio-emotional development of Erikson. His theory have people evolve by positionning themselves between two extremes in eight stages. Interesting fact, this is the only work of psychoanalysis that Piaget did not consider to be garbage.
