I have done much research on keywords and have found many with high enough demand and low enough competition to have the potential to be successful.

The question is, how do I use them? I have categories with multiple products and as many as 30 useable keywords. Should I use one or two keywords in the content or could I get away with using 5 or 6 without being considered "spaming"? Should I use one keyword and rotate content to use all of the useable words. Can I use keyword rich content at the beginning of each sub-category in order to "use up" my good keywords?

As you can tell, I need some help, and it will be much appreciated.