The Toptal.com blog has posted a guide to data encoding in PHP and MySQL looking specifically at the use of UTF-8 and related handling. They talk about some of the updates you'll need to make to configurations, code and the MySQL settings to fully support this character set.

As a MySQL or PHP developer, once you step beyond the comfortable confines of English-only character sets, you quickly find yourself entangled in the wonderfully wacky world of UTF-8.

[...] Indeed, navigating through UTF-8 related data encoding issues can be a frustrating and hair-pulling experience. This post provides a concise cookbook for addressing these issues when working with PHP and MySQL in particular, based on practical experience and lessons learned (and with thanks, in part, to information discovered here and here along the way).

They start with the changes on the PHP side, updating the INI settings to make UTF-8 the default character set and which functions you'll need to update and replace. With those changes out of the way they move to the MySQL side, changing up settings in the my.cnf file and a few other things to consider on the database side (including that the MySQL support for UTF-8 is only a partial character set).