Are you worried of those annoying ads on your Free Apps then there is an easy way to block them. There is an app called AdAway which will block ads from all free apps. This app will work only if your phone is rooted. If you haven't rooted your phone then surf on the web to find a way to root your android. The rooting process will be different for different manufacturers. But if you are not familier with all these stuff then get help from a geek cause a wrong way of rooting will make your phone an expensive paperweight so don't try your luck.
After installing the app press the enable ad blocking button, it will download some files from the web and then you will have to reboot your mobile. Any time you can enable or disable the ads but each time when you make changes you will have to reboot your mobile.

Here is the link for downloading Adaway from the market. Why you are waiting it's free....
https://market.android.com/details?id=org.adaway