On Flickr I actually started with ATCs. I was obsessing over them and doing heavy trading (are you sensing a theme here?). Between that and the tangling, I just got a lot of followers. I do so many different types of art now, that I think they come back just to see what the heck I’m doing now.
I also make an effort to do a certain number of likes and comments every day. I have a routine, and generally can get most of my socializing and link searching done within an hour while I have my coffee and breakfast. Once or twice a week, I spend more like 2 or 3 hours. I usually get on several times a day, to see who has responded to my posts, but try to keep those visits to 10-15 minutes or less if possible.
Of course, every once in a while I join a new group and just spend waaaaay too much time there.