Here are three resources for learning, or re-learning how to do a Reiki self-treatment.
William Rand demonstrates and explains the basic hand positions in a self-treatment. Follow along and give yourself a treatment. This is just an exerpt from one of his DVDs and so we only get to see a portion of a self-treatment. Still worth the time.
Here is a video of Reiki Master Teachers John Harvey Gray and Lourdes Gray, Ph.D. giving suggestions for practicing Reiki self-treatment in a class setting.