Advertisers are bidding on keywords. You are writing content for readers. Write the content for your readers. Go back after some keyword research and every hundred or so words try to put your keyword in there for your advertisers, but make sure it flows with your article. Also use relevant synonyms so when your page gets viewed google understands that it's a real site and not keyword stuffed... cause making a site stuffed w/ keywords for the purpose of adsense only will definitely raise red flags. You must please both Google & Your Readers... just keep your advertisers in mind. How to Make Money relevant words: earn good income, get paid, etc. If you can't use your keyword too many times because it can't flow, try to make it the URL, Title of the post.. then use it only once or twice more. Use your labels, tags conservatively.
If you are making a website, Then as a publisher it is your right to make the best site you possibly can. If you think about your readers and think to yourself why are they coming back? Are they getting what they need? Is this something i myself could find interesting? This will then keep pushing you to achieve the best site you possibly could, Organic SEO is vital yes but if you have a blog/site focused on giving the readers what they want keep pushing yourself to create the best content you can then you will find a natural following without using the search engines!