All you need to do is sign up with Ad Networks like HyperXMedia & RivitMedia and then place ads on your sidebar. You either get paid per impression or per click. Make sure you know which is the one that you are getting paid for.
If you are looking for tried and true tricks on increasing traffic to your niche website, then you are in the right place. Check out some of the resources listed here and the tips on how to use them for to your advantage.