The easiest way to fully utilize adsense is to start from scratch making adsense your starting point and target. You simply decide what ads you want to target and build around that. Then your SEO will match your adsense and you will be perfectly synchronized for both. For older sites that were built before adsense was used, you will never be fully synchronized, but you should try to improve as much as you can. Any improvement will result in more clicks! You can however improve 100% by starting with adsense first on all your new pages you add on now!
I like http://www.ranks.nl/tools/spider.html to use for keyword density. The only downside is that the page has to be public, so you'd better not start showing ads on it until you've optimized the page.