It's important that the website offers something that is kind of unique in its field. There are a billions web companies that offer similar things: SEO, web development, etc. A lot of people say that there is no need for any more of these types of companies. As true as that may be, it doesn't mean that a person can't have a site like this and be successful. If there is a new site to spring up that offers excellent tools, great customer service, and a dash of something that makes it unique, then I think it could be successful. I don't know what kind of business you're looking to open, but your website HAS to offer something special -- then it will market itself, seriously!
I am a writer on HubPages, and the admins there constantly tell us "don't SEO your stuff here, just write REALLY well" and I do that and I get real, natural back links. Take this example in your marketing efforts. Yeah, go ahead and market your site, I would! But if I were to come to your site, would I want to come back? Think about that as you develop your site and you'll find that it'll be a million times easier to market.
Exceptional customer service -> word of mouth advertising and referrals