1. Develop a good basic product/service. It doesn't need all the functionality, but whatever functionality it has (say the top 80% of functionality users use) has to be robust and easy to use.
2. Identify an initial group of customers that you can objectively identify and that you can reach. For example, students at Harvard (Facebook's initial users).
3. Work hard to get them to adopt your product. With so much noise, just making it free may not cut it. I know of an app in the truck driving space that physically went to truck stops and "bribed" truckers to download and try their app by giving away free food and T-shirts.
4. Once they are using your platform, you are getting the bugs out, and you are not losing users (i.e. they find it valuable), then you can think about trying to scale it.