We are all intrigued by our past lives, wondering what and who we were in the past. For the evolution of our soul, however, it is really not important "who" we were in the sense of a person (e.g. were we someone famous?), but in the sense of "who" we were as an essence. Therefore, the true questions to ask are "what have I accomplished in a past life", "where lies my connection in this life to my past lives", "what are the lessons I still have to learn, based on my past lives".
In this sense, reincarnation therapy is a valuable tool to help you on your spiritual path. Some people might claim that especially in the New Age, we should live in the "here and now" and not be concerned about our past lives. In my opinion, time is but an illusion, therefore, also your "past" lives are our "here and now".
I also believe, however, that nothing should be forced when it comes to past lives, and that the preferable method to delve into past lives is to stay conscious during the whole process. What you need for this process is a good past life therapist who will help you reach a meditative alpha state meaning that the right, intuitive hemisphere of your brain is more active than the left, logical hemisphere.
Your therapist will ask you for the picture you see (sometimes you may want to think of a specific difficulty in your present life and concentrate on a picture that will come up to help you resolve this problem). Unlike with hypnosis, you are awake during the whole process and truly experience and remember everything.
According to my experience, the ability of a person to see pictures clearly during their first past life session, has nothing to do with the spiritual background of that person. Sometimes people who meditate regularly (and meditating induces the alpha-state) do no see anything while others who do not practice any exercises and are not spiritually oriented see a whole past life unfolding in their first session. It may, however, take up to three sessions before you see any clear picture. If you don't see or feel anything after three sessions, you are doing yourself a favor by leaving it alone. There are many other ways to take on your spiritual path - regression into past lives is only one of them. And again - you should try this method only with an experienced past life therapist, who will also help you to keep your focus during the session. As this method is not using hypnosis and you are totally conscious, nothing that you cannot handle at this point in your life will come to the surface.
Very often, healing sessions induce spontaneous regressions into past lives. The regressions can happen quite spontaneously and not necessarily while you are meditating, but even while you do grocery shopping, driving home in your car, or something similar. In this case just watch the story that is unfolding in your mind's eye. Most of the times there will be one image that will strike you as having a relevancy to your present life, and many times you will have an immediate understanding of how this image is connected to your past life.
These spontaneous regressions come up as a result of a healing process that has been initiated in your system, and they are important in removing blockages and helping you on your way. Since these images "came to you" rather than "you came looking for them", they will never show up before you are ready for it and they will not do you any harm.
Now let's imagine you are still skeptical about past lives, and you are trying to validate if what are seeing are really past lives? If you do have these concerns you may be constantly blocking yourself throughout the process, making it more difficult. So just take a moment to ask yourself: Why do I see these images? What do they want to tell me? You don't necessarily have to believe that they are "past lives" - as mentioned before, time is an illusion. Just accept these images as part of yourself, accept that they are there and let them assist you on your spiritual path.