My site is already over 1 year old. So that 300 to 20,000 daily users did not take overtime. And my site pivoted several times. I initially created a platform similar to reddit. But now my site looks more of a social network focusing on people's profile.
I have a wide target demographics since I'm aiming to build a social network.
To get initial traffic, I researched what teens search online in the past 30 days. Then I posted Q&A posts on my site about all of those topic and answer it myself. I also posted links to my sites FB page, G+, Twitter and some of the bookmarking sites.
After 3 months, one of the Q&A post got #1 on google. I posted more Q&A related on that topic. And all of those posts are hitting top of google ahead of Yahoo Answers. So my traffic started to skyrocket.
Then I pivoted my site based on what visitors look for in my site. And hundreds started creating their own profile on my site.
Getting traffic is just part of the problem, conversion is the main purpose! So how can I make these people signup? My site is well designed so people will signup. And it's gonna be long to explain here. I spent a lot of time analyzing my visitors psychology.
Also the site should be easy to use. My site is fast and looks good on any devices. Actually most of my traffic are mobile. Everyone is on their mobile. So aim for mobile users! I'm also using FB/G+ oauth login so people can easily signup. And a lot of my members comes from FB login.