Send an appropriate content-type header, either via a meta tag in your HTML output...
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html lang='en'>
<head>
<meta http-equiv='Content-Type' content='text/html; charset=[color=red]UTF-8[/color]'>
...or via the PHP header() function:
<?php
header("Content-Type: text/html; charset=UTF-8");
Or use both if you are the sort of person who wears suspenders and a belt. 🙂