Spirits of our ancestors are probably one of the easiest we can get in contact. People serve ancestors for a variety of reasons. Whether for gaining the blessings of ancestors, finding out more of their lineage, using their aid in magickal workings and overall just continuing a relationship with them since they have passed on or igniting one.
Ancestral worship has been visible throughout history. They had maintained a state of Awe and respect over surviving family members whom believed they had authority over natural forces and spiritual powers. In olden days, Ancestors had their very own shrines within homes of their families or in temples where they were served as elders. They were called upon to help heal deadly illnesses, oracle or aid someone who has recently passed on.
Working with ancestral spirits is quite easy. Gather the names of passed on family members. Write out a personal report for each of them: Where were they born, whom their spouses are, when did they get married, their children, etc. The whole nine yards if possible. Talk to family members who had known them when they were alive and get ahold of what they had liked.This is more of to get an idea of how their character is like as well as to make sure you are talking to the right spirit.
The next would be to build up an altar for them. Keep a picture of them on it and everyday(if possible). Talk to them on your problems, seek out their blessings and meditate with them. You could also AP and meet them or in your dreams for that matter. Offer them something daily such as burning incense for them. Serve offerings on special occasions for example food they loved best when they were alive. Soon you'll develop a strong relationship with them and unexpectedly meet other ancestral spirits.