You really have to ask yourself this. It's like you wrote the greatest poem of the world, but nobody read it. Your website is a mirror of your business, and it equally should keep your old clients happy and informed, and attract a bunch of new ones.
And that's were search engine optimization (SEO) comes into play. SEO is what can turn any obscure website, into a popular one. SEO can bring you many new visitors, that can potentially turn into new customers.
ATTENTION: SEO is not about getting the #1 spot on a certain search engine for a single term. Nobody can guarantee you the #1 spot. (You can get there, depending on the competition on that keyword, but it's not guaranteed.)
The best way to optimize an website, is to create it, in the first place, having SEO in mind. Your website can benefit a lot more from optimization, if its code is clean and well organized, the content is well written, and the pages are targeting keywords/phrases that best describe your business. A good SEO strategy should start with analyzing the field of your business, the competition, the most searched for keywords/phrases for that field.
SEO can be applied to existing websites too, by analyzing the overall quality of the content and structure, and making adequate changes to it.
Here are a few clients, that have already benefited from our expertise in SEO: