Once you have your keyword targets, your content created and your site structure established you must now move on to the most obvious step, the optimization of your content.
As noted above, a spider places importance on what it reads highest on the page and so beginning with a sentence that includes your targeted phrase only makes sense. That said, stuffing in keywords in hopes that it will add weight to your page generally doesn’t work. The term "keyword density" refers to the percentage of your content that is made up of your targeted keywords.
There are optimum densities according to many reputable SEO’s though exactly what they are is debatable. Estimates seem to range anywhere from 4 or 5% to 10% to 12% (quite a gap isn’t it).
Personally, when it comes to keyword density I prescribe to one rule: put your keywords in the content as much as you can while keeping it comfortably readable to a human visitor.
Some do it first, I do it last. Regardless of when you do it you must choose your heading. At the beginning of your content you have the opportunity to use the "H1" tag to specify the heading of your content. This tag is given extra weight and is also an indicator to the search engine of where your actual content starts. Make sure to use your keywords in the heading but don’t shy away from also adding additional words (though not too many).