First and foremost:
Put your efforts into taking better and better photos. Try to be humble, and Learn from the masters.

and then, (further to coollibrarian's answer) :

buy a pro account;

update and expand your flickr's profile page

take and post more photos, at regular intervals.

add better titles, descriptions, and tags to your photos.

reply to those who comment, fav, tag, or "note" your photos, and check their flickr streams 

look for like-minded people who share your interests and hobbies,

browse flickr, add faves , comments and tags to others, add contacts and keep in touch with their photos;

join groups where you have to comment   or  score other's photos , and then they will do the same to you;

join groups with a high number of members;

join theme-based groups, contests , location-based groups;  

join the discussions at your favorite groups. 

start your own niche group, choose an interesting theme, and invite others to join.

Post photos at your blog and link them to their flickr page;
Display the link to your flickr stream more prominently at your blog and photo-blog.

visit other peoples photo-blogs, join the discussion and sign with a link to your flickr page.

good luck !