Well, since
isiscolo started it, and because I've switched to filtered posts, I'll explain my friending policies.
I'll be a little less thorough, because I'm tired tonight.
I friend everyone who friends me. It's a bit of a game I play. I look at your friendslist and the communities you're part of and try to figure out... "now how did this person find me?" Usually there's a spate of friendings after I post a new fic so it's easy to tell, but some of you come out of the blue.
I used to have everyone on the same list, but I was missing posts from the people I'd followed for months. They just... swept by in the flood.
I know how to filter my posts, but I still haven't a clue how to switch filters on my viewed friendslist. So I set up my default list to include my first 40 or so friends and the authors whose stories I'm reading at the moment (can't miss those updates!). Then I log out to see everyone else. I check the general filter about every week or so, more when I'm fucking off. ;)