Kenny's suggestion is really the way to start with responsive templates. I followed that route a while ago.
I would like to contribute with two details:
The meta tag allows to scale the screen size
meta name="viewport" content="width=device-width, initial-scale=1"
jQuery provides clever templates, valuable when combined with viewport
link type="text/css" href="http://code.jquery.com/mobile/latest/jquery.mobile.min.css" rel="stylesheet"