A good Search Engine Optimisation agency will help you understand what your customers are searching for in the first instance. The terminology you use to describe your product, service or content is often not actually what people are searching for on Google/Bing/DuckDuckGo.
The trick with SEO is finding the right tradeoff. You need to target terms which people are actually searching for, but where there isn't so much competition that you don't stand a chance.
So, as an example, my startup 3sixty used the tagline 'Anonymous feedback fast', which was plastered all over the home page. With a bit of help from an SEO expert, I'm now changing it to '360 degree feedback', because (a) that's something people are actually searching for, and (b) it has a fair bit of competition, but not so much that I don't stand a chance!
A good place to start is SEOmoz's Beginner's Guide to SEO.