When do we reincarnate?

I just had the flash that we go into another body when the planets are in a position where they will facilitate our evolution. I do not think it is random process. It must be like trying to jump on a moving carousel. We choose which horse we want to ride on and jump on. Obviously we have to be conceived, but I do not think that it is random. I have often heard that we choose our parents and that would make sense, because we would have to be preparing to enter back into the world. It is a magical process that is beyond my ability to comprehend.