Archive.php help

Hello all,
I have the default archive.php template all made up. My client has asked that if there is a post which has more than one page, a link be provided reading “NEXT PAGE”. If the post is not paged then nothing will be showed. I’ve been trying various things for the past couple days, and I’ve just not succeeded. Can anyone point in the direction/provide an example of how I might achieve this?

Thanks,
Stephen