I ....
1. Comment on other peoples photos because I like them.
2. Stay clear of groups with any sort of stupid graphic or post 1/spam 15
3. Never add contacts who have more than 150 contacts themselves as it means they are highly unlikely to comment regularly on your stuff.
4. If someone adds me as a contact, they need to have commented on my work otherwise I won't just immediately add them in return.
5. When I do add a contact, I put the effort in to comment on their work.
6. Look at local groups to where you live; add contacts based on that.
7. Anyone adds a graphic in a comment, or even a self promo graphic ... its toast

8. Maintain a manageable balance of contacts. Anyone who I have known for a long period of time gets promoted to a 'friend'; anyone else a 'contact'. I regularly comment on most shots that are in my friends thumbnails list. I periodically comment on the stuff that is in my contacts, again this is based on me liking the shot.
9. Negativity - I have many contacts who I can critique with no awkward reaction. This is something you kinda adopt once you know your contacts for a while. When I started, I had someone really fly off at me and was really quite abusive, as I said the 'horizon was wonky' on one of his shots. I had to block him in the end.
10. Meet up with some contacts; I have a few really good photo buddies as a result of Flickr.
11. I know it sounds odd, but its also about how frequently you post to Flickr. I try and keep the momentum going, so not going more than two weeks without posting. This means you maintain contacts; so they don't forget about you. If you are a contact that appears in someone elses thumbnails every couple of months, then you will just get forgotten about.
12. Spend some time going through the photostreams of those who you do add as a contact. I generally always do this. I will spend some time commenting on the older stuff too.
13. If you do the above, you will naturally recognise your contacts contacts. They will recognise you (as you will comment more regularly) and then in turn you add each other as contacts. I have many contacts of contacts of contacts. When someone adds you as a contact now, the email you recieve shows you who/if they/you share contacts. This also helps with building up a little following.
14. Don't let it take over from actually taking photos.
Hope that helps matey. If you ever fancy an afternoon/evening/day out taking some shots, give me a shout.