How to ensure apps get uninstalled cleanly? I use to try (install and remove) a huge lot of apps to choose the ones I will actually like. I am afraid uninstalled apps can leave some residuals behind and this can crap up the system in some time. How to make sure this won't happen?
Before uninstalling the app, go into the App Info, force stop the app, clear the cache and data, and then Uninstall. 

This is not 'guaranteed' to remove absolutely everything, but it should be a lot cleaner then just uninstalling it.