Here's a trick: Make sure you choose one SEO keyword as your focal point per section.

Then build around it.

Simple? To the point? Yes, it is. And it makes more sense than throwing together a jumble of keywords into one section. By focusing your writing around that one words (and using a related term or keyword to beef up that section of content), you'll keep the section readable and be able to maintain your keyword density by eyeballing each section. If you feel there's too little, you can add your terms where appropriate. Too heavy? Either add more content or remove a use of that particular keyword to lighten up the density.

Check out this SEO site for a Florida labrador breeder to get an idea of what I mean.