This post explains the fundamental differences between character sets used on your website. Here is the most popular charset definition that should be placed in the within the HEAD tag:
<head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">...</head>
For ASCII characters the following code can be used:
<head><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1">...</head>
