There exist different types of regressions. They can be executed with the instruction of a hynotizer or a therapist (I do not know many of these ones) or by yourself. Even when conducted on your own there are divers possibilities: solely by yourself or with the help of spirit guides what signifies a further meditation within an already existing meditation phase. In both cases you will end up in an out of body experience. I find the method involving spirit guides too complicated. Usually I do it on my own without means of help and may also give an instruction, if somebody would like to try it out. It does not harm.
First of all, a correct meditation is the most important. The easiest form, also called transcendental meditation, is satisfactory.
This is a short instruction to it:
Look for a silent place where you are undisturbed from environmental noise. This can either be a room to be locked with a key or also another quite place in the nature e.g. under a tree.
Assume a comfortable position to get fully relaxed. Lay either at the bottom/meadow or sit down without force. I prefer the lotus position or sitting on the heels.
The hands should rest in the lap. The open palms should be placed one over the other, the both thumbs joined in the middle, so that the hands constitute the form of a triangle. This cares for a constant, uninterrupted flux of energy.
Now close your eyes to avoid the influence of light. Do not press the lids of your eyes, just close them gently. Everything done compulsory is not recommendable for meditation.
The most difficult for a lot of starters is to empty their heads. This can be easily achieved by controlled breathing. Again, there exist different possibilities to gain a controlled rhythm of breathing. I mention just three different, hoping that anybody will find the most corresponding: Counting, Visualisation and Noise Perception.
Inhale deep by your nose. Leave the breath a while in your body and count till 10. Then exhale loudly by your mouth.
Inhale deep by the nose. Imagine the breath to be a white lightening beam which strikes down from above to the bottom, around the navel and then returns again as a light beam. When the lightening is above again, exhale loudly by the mouth.
Inhale deeply by the nose. Imagine the breath to be a wind, hear how the breath howls and browses. It "storms" down to the navel. There it is tossing. You can hear steps when the breath slowly returns above. Then you exhale loudly by the mouth.
After some time, you have got a rhythm. Concentrating on controlled breathing does not leave any space for other things in your heads.
Based on this now the regression:
Concentrate now on your "third eye" while meditating. The "third eye" is the so-called "inner eye", the spiritual vision. It is situated on the middle of the forebrow between the two "real" eyes. Concentrate very strongly on this spot, do not think anything different!
Suddenly you will notice a path of light, like a tunnel which leads out of the third eye. Concentrate on the path, follow it. Until a door that you will open then. When you will open the door, it can happen that you perceive a lot of stimuli: Different voices and noises, different colour flashes (mostly red, white or yellow in my case). This is the moment when your aetheric body leaves your physical one. You leave your plane and arrive to another one.
At the place where you see pictures materialise again, observe everything exactly! It is one of your previous lives. Memorise what just happens, what people do, what clothes they wear, where everything happens, who is also present etc., because you will never know if you ever return to this spot.
To return go back to the door and open it, go through it, back along the tunnel and through the third eye. Open slowly your eyes and stretch a bit. Tak a little walk or just relax, depends on you either feeling exhausted or refreshed afterwards.
When doing it the first time, it might happen that it does not have the required effect. So please do not lose patience and try again and again. Do not make it a "must". One time, you will get it as Rome had not been built up in one day.