Someone who remembered former incarnations from self-initiated regression might say meditation is a way to go. You will need to enter a state of mindfulness, avoiding all external influences, and then clear your mind of conscious thoughts. Then begin to focus on a spiritual journey which is not too different from astral projection.
Once you get into that semi-hypnotic state between wakefulness and sleep, try to mentally create a hallway through which you are to pass. Imagine it vividly so that you can use the same astral image every time you want to explore your previous incarnations. Now will your astral frame to walk this hallway, open the door at the end of it (and open your mind with it), being ready to accept whatever you may be able to see.
At first, the images, sounds and sensations may be as simple as smelling the ocean or seeing the color red, the feeling of petting a dog or observing an old house that used to be yours. Sometimes, you may face past life memories that are a lot more vivid and a lot less pleasant.
People who remember past lives through meditation stress that you must stay focused, keep your mind open, and accept whatever comes your way. Let memories randomly appear and disappear, as if on a computer screen. Don't question what you see - you will have plenty of time to do that once you're back from your hypnotic trance. Be receptive and you may discover information well beyond your highest expectations.
With practice, images and sensations will become stronger, more detailed and, with them, your connection to your previous incarnations will blossom. Persevere and you will have some fascinating experiences in your self-initiated past life regressions.