Alot of time people undertake vision quests or trance work to contact ancestrial spirits so I would start there. There are also rituals that help you to do this as well. For instance Samhein is all about gaining contact with the ancients and there are alot of rituals for that particular day that deal with the subject.
Dillon is correct. Trancework and vision quests are popular means to make contact with ancestral spirits. Also if you really want to make this a regular thing make an altar dedicated to your ancestors, learn about your ancestors, and explore your past. Visualizing and focusing on an altar dedicated to your ancestors will aid in contacting them. In the Northern pagan tradition ancestral spirits are honored almost the same as a deity would be. Make acts of respect and honor for them and give them offerings. Good luck!