I recently wrote about some WordPress trouble a client had that was related to the database size. I listed some SQL commands that can be run, but there are simpler ways to keep a WordPress database clean and optimized to avoid trouble like that.
It’s good practice to install a plugin like WP-Optimize that can perform the same tasks without the need for nitty gritty SQL commands. Not only will your database not fill up, but keeping your database optimized will also make sure your website / blog loads as fast as possible.
WordPress also has a feature called “revisions” that can unnecessarily clog up the database. You can only turn that off by diving into some PHP files on the web server, which isn’t for the faint of heart. For more information on doing that, head over here.