Family: A strong family life can enrich retirement, while estrangement, feuds or simple neglect can create a void, Warner said. Future retirees can start now to ease strained relationships and strengthen existing ties. Visits, letters, e-mails and family reunions can build long-term bonds.

Friendship: Warner advises a lifetime pattern of making friends with people both older and younger than yourself. Older friends can give insight on what aging can be like, while younger friends can help keep you flexible and more in touch with the world around you. Those who make friends only with people their age can find themselves just as lonely as those with no friends as peers begin to die, he said.

Learning: Scientific evidence increasingly points to a "use it or lose it" approach to brain function, Warner said. People should challenge themselves mentally throughout their lives to keep their minds sharp.

Interests: Happy retirees tend to develop outside interests well before retirement and say that some kind of absorbing activity--a hobby, volunteer work, travel or even a new career--has energized their retirements. Those who wait to pick up a hobby or begin volunteering may find themselves unhappy with their choices or unable to find their niche, Warner said.