Promoting a website is the same as promoting any other product:

1) Identify your target market 2) Find a distribution channel 3) Pursue your target market

Many startups go the TechCrunch route, but unless your target market is Silicon Valley technologists it's probably not a smart move. Put another way, not all customers are created equal.

When I was first launching Appaholic (now Adonomics) I posted aggressively in the Facebook developer forums. Beyond that I pursued SEO.

Most startup people I know think a bit about (1), very little about (2), and jump right into (3). Be methodical and data-oriented, instead.