I've been doing SEO for years and I'm No.1 for a lot of keywords for a number of sites which is what Google relies on to list your site in the correct search. That is the first step, ensuring the search engines log exactly what you site is about otherwise you might have a widget site that is never listed in widget searches, but appears under apples!
Part 2 is then moving up the rankings for those keywords, and for that you need backlinks using related keywords, preferably from higher PR sites, and especially from .gov & .edu