For apache just go to your httpd.conf and edit the line:
<IfModule mod_dir.c>
DirectoryIndex index.html index.wml index.cgi index.shtml index.jsp index.js index.jp index.php4 index.php3 index.php index.phtml index.htm default.htm default.html home.htm
</IfModule>
You can copy the one above it's a good set up.
This is good to work with since you want the extension you are using most to be in the front for better loading speed.
-Charles 🙂