An example: My Ascendant is 18 Gemini . . . reversing backwards through the natal chart, we come to my natal Sun at 17 Aquarius (121 degrees in a clockwise fashion from the Ascendant)
based on my theories, this number "signifies" a past life -- so (for me) 1955 - 121 = 1834
the planet is in Aquarius and the sign on the House in which it is housed is also Aquarius; the 9th House is the "natural" house of Jupiter and my planet Jupiter is natally in Cancer (and the sign on the House in which it is housed is also Cancer -- although the sign could be "intercepted" and so there could be two signs here)
so based on my "theory" I will have a past life, born in 1834 who was either an Aquarius or a Cancer
based on the relationships of planets to house "rulerships", with this person (since the Sun is the planet) we would look to the 5th House, where we find Neptune in Libra (whose home is the 12th) and the Vertex in Scorpio (who is most at home in the 8th)
also, the Sun is LEO so looking for any planets in Leo we find the Moon in the 3rd and Pluto in the 4th (Moon natural home 4th, Pluto natural home 8th)
there is method to my madness . . . so this person has a strong water element to his or her chart but the 8th House is the one with the most "action", the House of Death and Pluto, the ruler, is in Leo
so a King in the House of Death . . . perhaps a spiritualist or perhaps a person whose "profession" involves Death in some way -- an undertaker or perhaps a professional soldier
and we could continue to drill down (too long for this post) to refine the elements and make some suppositions as to profession, location, personality and even "life span"
it just turns out that I have ALREADY identified a potential past life, an Aquarian (who shares the same birthday as me) born February 6, 1834
a professional soldier, named William Dorsey Pender and ID'd as my past life by several very well known professional psychics over the years, including Allie Cheslick and the Psychic Twins
. . . and to some mild degree he WAS a bit of a king, as he was a General in the Confederate Army during the Civil War
this is but a peek into how past lives are laid out in the natal chart and how I "recover them", not only the how and why but, with incredible "detail"