You can get lucky and pick the right niche and get their quick, but more than likely you are going to spend hours and hours of your free time when you aren't working a real job doing tedious work on your site(s) building content, and inbound links and doing the necessary social media work like facebook posting and twitter, etc.
Building a website that can at some point rely largely on volunteers and or user generated content is the best way to go in my opinion. Forums for instance, if you can have a successful one in a high paying niche are a big help in getting the ball rolling.
The bottom line is it does not happen overnight. If you pick the wrong niche(s) you make work for years and never even get close.
I'd suggest doing some serious research to find a niche that fits two criteria:
It must be relatively high paying. I'm not talking 20 dollars per click or even 5 dollars per click. Just something where you can at least make 50 cents to a dollar per click with adsense but can build up a decent userbase and subscriber database.
The second would be something YOU ENJOY DOING. Pick a topic you enjoy talking about, reading about, writing about, etc., so that over time you can become an authority on the topic and will not get burned out working with it day after day.
