Maintain Your Search Engine Optimization
A. Check your incoming logs.
If you are getting several referrals for a niche topic. Write more on that topic. Obviously your visitors want that. And more or that will lead to more quality, targeted hits, which is what the point of search engine optimization is after all.
B. Add content, add more content and add more content.
Stagnant sites tend to loose search engines' interest. If you want to get ranking with the big guys, you've got to keep up. Keep adding quality content and articles on your topic. Search engines and visitors both will be more likely to stay around.
C. Validation and HTML.
Continue validating pages and cleaning your HTML starting with your top level pages and moving down.
Continue to find and submit to new directories and upkeep paid directories as necessary. Continue to look for appropriate topic specific directories. Check your submission list once every 6 months to a year and resubmit to directories that did not accept you.
Continue to harvest quality, inbound links using tips outlined in Step 6.
F. Keep up with changes.
Search engines tweak, improve and change their algorithms often. Keep up with the changes.