Earning from free blogs

Hi,
I have some free blogs i.e. blogspot or wordpress but I'm not earning any thing.
Please share any trick to make some cash from my free blogs.

Thanks

there are no tricks there is just one condition
quality content and backlinks = traffic and money

Is your content unique? What have you done to monetize your sites? What have you done to promote your sites?

These are some keys to think about .. with traffic comes money.. you cant just throw up some sites, stick some adsense ad's on there and expect to bank