Look at the friends of people you have just followed.
Look out for people who have criteria for following others e.g. I
will only consider following you if you have ever replied to me (and
made me laugh out loud)'. Satisfying the first is easy, the latter
less so.
Scan the Public time line. Occasionally, you will find a gem in the
fast flowing river.
identi.ca currently doesn't have an 'Import my friends' but they
will undoubtedly use the same old tired nickname with the same old,
tired profile pic.
Old technology, admittedly but you could email an invite to friends
who might be interested.
Never, ever unsubscribe from anyone. This is easy on identi.ca as
this is not currently supported..
Use searches to find like-minded
individuals talking about common subjects of interest.
If you stumble across interesting content on another service
(FriendFeed, blog, Twitter) with a link to their identi.ca profile,
follow them.
Blindly follow anyone who replies to your posts.
Look out for people located close to you (town, county, country).
Do not troll for followers on other services although subtle,
understated evangelism may prove worthwhile.
Do not, ever, under any circumstances, beg or plead for followers.