keywords usage

I have properly optimised my page for 1 keyword and was wondering if I throw in other keywords naturally in the description with anchor text, would it then be possible to rank for the other phrases too if they have not been optimised anywhere and only mentioned in the description with anchor text. So would it help my page at all or is it just a waste of time to add related keywords in the description.

As long as you don't overoptimize each additional keyword/phrase then you can theoretically have tons. I have a gaming site that uses several keywords per article to rank other articles. Just make it natural.