when we talk about keywords, we do not mostly just mean individual words, but phrases. A couple of things here. If your checking your logs, then great, as that will tell you what people are finding you for. But you ideally need to find out what they are NOT finding you for, but finding other people for, as your site is not appearing in search for those phrases.
A typical web marketing /Search Engine Optimisation (SEO) campaign would run like this: -
Learn about the business
Research keywords using tools like this http://www.digitalpoint.com/tools/suggestion/
Examine existing site, or plan new site around these keywords, grouping the keywords into workable groups for per page.
Build site around keywords ensuring they appear in the page title and in the copy of the pages
Add extra pages to accommodate all the keywords found, ensuring they are built around useful information for the visitor
Ensure navigation structure is simple and easy to follow and uses keywords as anchor text where possible without sounding odd.
Develop site map linking to pages using the anchor text keywords for each page, also with a description of the page being visited.
Upload the site
add links from directories etc using keywords as anchor text where possible.
You say 'should I add them to my keywords' I am assuming here that you are talking about your keywords meta tag? If so that really does not do a lot for google, and simply adddingthe words to your keywords meta without them being in the title and the page copy is also not likely to do a lot of good.
I have probably raised more questions than I have answered here, so feel free to post any questions you might have. (apart from who taught me to spell and compose a sentence