Link building is one of the most essential factors of SEO. There are several simple things you can do every day to keep your link building strategy effective. Keep a log of dead, irrelevant, poor links and prune them appropriately. If you have more than 25 links, creating a directory could help in managing and organizing the links. If you decline a legitimate link request, be sure to write an email to the webmaster explaining your decision.
Make sure your links are working properly, relevant, and sending traffic to your website. If they are not, take the time to fix them. You don't want links that are dead, pointing to irrelevant content, anything of poor quality, etc. It's also a good idea to keep track of the websites linking to you. Regular pruning of dead, irrelevant, poor links helps keep your link portfolio healthy. Also, ensure links are labeled to adequately reflect the webpage they link to.
As your links grow, you'll want to keep adding new ones, ordering and categorizing them, and placing your best links at the top. A good rule of thumb is to have no more than 25 links per page, creating additional pages for the rest of your links. You can create a directory of your links to help manage and organize them as your list grows.
Respond to link requests in a timely manner. You may get many spam contacts, which you should have a system in place to track, block, and otherwise handle. Other link requests may not be a good fit, so be sure to assess each legitimate request. If you decide to decline a legitimate link request, be sure to write an email to the webmaster explaining your decision. If the site is related to your website, they may be able to make changes and become a valuable link partner. Common courtesy goes a long way, especially in today's world where it's becoming less and less common.
Make sure your website is up and running, inspected for issues, and updated on a regular basis. Also, make sure all incoming and outgoing links are relevant to your website.