I pretty confuse on your post,. Are you asking on how to improve your keyword with the factor of keyword density? Or you want to improve your keyword in SERP,., Anyway, keyword density is the number of times your keywords is repeated within the page. So know the right percentage of the keywords should be appear on the webpage. Anyway, I don't think keyword density plays an important role now in google. What matters for me, is the number of quality backlinks.
there are a lot of tools for checking your keywords you may find them on net chk dis 1:: http://www.seocompany.ca/tool/free-seo-tools.html
www.webconfs.com has a great tool for checking your keyword density, i suggest it should be around 5-7% of the overall text on that one page, the tool shows you how much it is. To increase it, you just need to edit the content and add a couple more key terms however not too many that you over do it and it becomes annoying to read and makes your users run away. Will.
I'm having a bit of trouble developing my initial seed keyword list. I'm confused as to what keywords make a good seed list.
You want the keywords to be relevant to your site, highly searched words however not too competitive to rank highly for.
Keyword tracker is a good tool to see how many times each word is search daily. I would also advise using this aswell http://freekeywords.wordtracker.com/ Will.