It's very difficult to train your mind separate from the Aikido you plan to train in because it is relative to those actions and events that take place within the dojo or between you and your partner at that particular moment. Having said this, I believe it might help you to practice either Zen meditation or Vipassana meditation in order to develop concentration and clarity of mind. In Vipassana meditation you can also investigate your concept of yourself, what motivates you, and your reactions to aversion. But even this is difficult to do from a book. You should seek out a community of meditators who can guide you in this in lieu of an actual teacher (which are difficult to find). Where are you located? Perhaps I or another can refer you to a legitimate meditation teacher.