Keyword density isn’t as important as it’s made out to be. Some people really go crazy with 10-15% density, but it’s really challenging to write coherant copy with that type of percentage. You will also notice if you do a few searches that the density of the top returning sites will be all over the board from 15% down to 0%. Where you rank it the SERPs has much more to do with backlinks. You should write your copy for real people, making sure to sprinkle in your keywords here and there, definitely put them in the title tag and emphasize them on the page. That’s about all you really need to do.