There are different theories about the spirit world and reincarnation. It depends on who you ask about their personal experiences with the spirit world and their belief system. 

My own personal views are, "We are all spiritual beings having a human experience". We live many lives on this earth and we keep coming back time, and time again," To grow and learn". We quite often choose the same spirits to share our human experience with, and can be born into the same families to assist us in our growth process. Our goals in any lifetime (in my opinion), are as follows:

To Grow and Learn
We achieve this by selecting who are parents will be, our ethnic origin and major life experiences that we want to experience in this life time. When we are born, we start to forget who we really are and adapt to our new lifestyle, family and our role.

To Become Non-Judgmental of All Types of People
We achieve this, by coming back time and time again in different roles. For instance, if you were a thief in your last incarnation, you might be a police officer, an attorney or a judge in this one. If you were persecuted for your race, beliefs or occupation in your last human life, you might decide to see what it's like being the persecutor in this one.

To Practice the Art of Humility
People who achieve true humility have achieved "Divine Oneness". Think of people like Mother Theresa, Ghandi, Nelson Mandela, Martin Luther King, Bobby Kennedy, Louise Hay, Wayne Dyer and Eckard Tolle. These people are prime examples of what we are all working towards. Remember you don't have to be famous for your actions. You just have to ensure that you practice true humility with all people in your world. Once we have archived true humility in all matters, you can ascend into the Divine.

Past Life Memories
You may remember people, places, or things from past lives. This is often referred to as "Deja Vu". Or you may meet someone for the first time and get an instant like or dislike to them. This could be from a past life experience with this person. Our greatest teachers are people that are sent to try us, are quite often appear in our lives so we can learn our life lessons.