For me it's having my own space, working as short hours as a full time job goes, being financially secure, seeing my family often, and having a partner that's away most of the time. The word loner has a lot of negatives around it, but it's probably what I am. I enjoy company, but I do like not having to answer to anyone often.
It's different for everybody, but don't just go with what society tells you. I was in (different) relationships from when I was 16 until I was 21 before I realised I hated it. Now I have a much more casual relationship.
Self discipline is a key thing too, actually doing what you want to do rather than vegetating in front of the TV from apathy.