I don't know - why you ask such a dumb question? Obviously its content - and learning how to spread your links.
Really it is more about creating an online web presence, creating a community and offering helpful useful information that would be of interest to potential customers. Before you start figure out what you want your website to accomplish and then build from there. You can use social media for marketing etc...
Well, it all depends. One of the fastest ways to get traffic to your site is by having articles written revolving around your niche and submit them to article directories. These articles can get picked up by search engines and can rank high in their results if you know what you're doing. Depending on your niche, you could get tons and tons of traffic if you release enough articles.
Start with UsFreeAds unlimited only for $9.0. Write a small paragraph.....an AD instead of doing a full blown article.