Would Effective Advertising Make Net Profit?

I hear all over the place that if you advertise effectively, you can actually make a decent return, simply by having advertised.

For example, a lot of sites and networks seem to offer incredibly cheap advertising that would almost have to give a net profit. Even here on Warrior Forum, with high quality traffic as compared to many other sites, the cost for 300,000 impressions for the given price would seem to be a great investment if one could afford it and had a high quality site on the other end.

However, I was actually thinking of trying out Reddit to start with. I do frequent Reddit, and their cost for 1000 impressions appears to be very minimal... Has anyone else tried advertising on Reddit, or here on Warrior Forum, etc? How did it work out for traffic to your site, as well as revenue? Thanks so much!

P.S., I have looked around for info on how to advertise more effectively, but what sources would you guys recommend for help in this area?