If one wants to attain a top ranking for the most popular keywords or phrases on any web page I agree it can be difficult. However, if you get very, very specific within that group of keywords you can get amazing results assuming your page is set up properly for high search engine rankings.
Don't just try to get the top ranking for "watercolor paints".
Instead get more specific: "Reader's Digest complete watercolor set by David Norman" for example.
You may not get near as many searches but you will probably get top ranking and most if not all of the searches looking for this exact item.
We have been very successful doing it this way and recently was able to get a number one ranking in google for one of our products in less than 5 days.
NS makes this much easier for us because of the way the URL's match the items on the web pages (if set up correctly). Each page should have one theme and all of the SEO info should complement that theme, with the URL, meta tags, content, alt text, all having very similar words/phrases. We try to make sure that the keywords used in the META tags are listed somewhere on the page and the top one or two are on the page more than once.