If you have a self hosted WordPress blog (so not hosted on WordPress.com) there are important tools you should use to keep it health, over the basic tasks you must perform (keep your WordPress blog version, themes and the various plugins always updated).
More articles you have published more you need to do maintenance.
When the articles are a lot it’s difficult to keep track all the links inserted.
A great tool (available as WordPress plugin) is Broken Link Checker, it performs a scan of all the links (images includes) and notifies if they are no longer valid / unreacheable.
If your media library is becoming huge another good plugin is WP Smush, it optimize all of your images by resizing them.
It’s important to do maintenance of your WordPress database. A fully featured plugin is WP-Optimize, it has various clean options (post revisions, auto drafts, spam comments and comments in trash, unapproved comments, etc…) plus it allows to optimize the tables of your WordPress database.
Security is an important topic. Expire passwords plugin asks users to change their passwords on a regular basis.
If you use Google Webmaster Tools check periodically that there aren’t problems.