Study your subject. The first step in being able to teach anything successfully is knowing your subject. You should have a strong foundation in psychology as well as a good knowledge of the sports psychology specialty.
In the Internet age, courses leading to undergraduate, graduate and doctorate degrees in psychology, are easily available without needing to physically attend a university. Online sports psychology courses are offered by some colleges and universities online.
Obtain the certification needed for teaching psychology in your state at the college or university level.
Join the Society for the Teaching of Psychology (STP). Membership is available for those who are involved in teaching psychology at all levels, and they provide a magazine subscription and newsletter with helpful information that comes with membership. The STP magazine is full of ideas in learning techniques and methods to fine-tune your teaching.
You might also consider joining the Association for Applied Sport Psychology (AASP), which offers membership for professionals as well as for students. It is the largest organization in the world for sport psychology professionals and students and is interdisciplinary, drawing from the fields of exercise and sports, as well as the practice of psychology. Membership can help you to keep abreast of scientific developments in the field, and help to keep your teaching fresh and interesting.
Read up on sports psychology from many different angles. Sports psychology is not just knowing how to become the best athlete, there are many angles from which you can pursue the subject. By reading a wide variety of ideas on the subject, you will be able to help students to think critically and develop their powers of reasoning, present a balanced and realistic view of sports, rather than a glossed-up version.