Being friendly doesn't mean going bar hopping or inviting them for Thanksgiving dinner. It means treating the volunteers in a friendly and respectful manner. Volunteers serving on a committee don't need to be close personal friends with the chairperson to do a good job. Invest your efforts in loyalty. Everyone, staff and volunteers alike will note your behavior.
Loyalty begets loyalty.
All volunteers value evenhandedness. Treating people fairly doesn't mean everyone gets to do everything, but it does mean that the leader is equitable in decisions. Being fair increases credibility. Know when to get help and from the best. Leaders are always willing to ask for help.