The reason we are here on earth in the first place is to learn and develop our own spiritual growth, although we may not be aware of it. The information I received from my guides is that we choose when we want to come back, when we are ready to come back and we even choose our own parents and the type of life we wish to live, we choose these options based on what we need to learn this time around or rectify any mistakes we may have made in a past life, for example lets say we were born into a rich family in out last incarnation, we had everything we needed nothing really to worry about, yes we may have learned from this experience, our experience in that life could have been one of wealth or even greed, if it was one of greed then we may choose our next life as one of hard work and poverty so we can appreciate the wealth, of course this is just an example.
As we have only one spirit "the real us" which again from what I have been passed on from my guide our spirit is neither male or female, sex usually only defined by the physical body. Although if we come back over many life times as more male or female our spirit can take on that identity as either male or female. This was later explained my guide saying "Why do think a man can love another man and woman love another woman" then it kind of made sense after a lot of thinking. If our spirit becomes predominantly female and we are born into a male body, this can cause the man to have female feelings, like a man falling in love with another man or even sometimes they get confused and even have a sex change, the same goes for a predominantly male spirit in a woman's body, again a woman falling in love with another woman or being like tomboy.
Another issue with past lives is our health, a few years ago I did a reading for a lady quite by accident we met in a pub and I saw in my mind a vision of her being run over by a horse and cart, the wheels of the cart went over her back, I knew this wasn't going to happen as I saw cobbled streets and everything looked old, I mentioned this to her and to my surprise the previous week she had been to see a hypnotist for past life regression and she experienced the same vision in the fact of the horse and cart knocked her down at which point she passed over, my point is here that in this life she was suffering from a bad back from an early age, so it seems that our past lives can affect our next ones, even if on a subconscious level our past memories can cause physical symptoms from a past life.
There are many ways to find out our past life's, from dreams, regression and visions. Just out of curiosity take a look at your health problems or phobias in this life, especially if they were from a young age, phobias in particular are interesting I once worked with a hypnotist as I was learning about it at the time, and one subject he had was afraid of snakes although he was unlikely to encounter one in normal life, he would still freeze up and start to sweat if he saw a picture of one. The interesting thing here is when he was regressed to a previous life he was actually working in a jungle and was bitten by a snake which in turn he passed over due to poisoning. With this in mind our phobias may give us a clue to how we passed in a previous life, this of course doesn't mean all our little phobias may be from a past life, but the evidence there is quite interesting don't you think?