You should carefully consider whether or not to monetise an App. For the most part, advertisements in an App is a massive turn off for most people. Personally I hate them.
A better approach (and this is just my opinion) is to make your App free and restrict access to functionality by making use of InApp purchases to unlock those restrictions.
If the App is constantly throwing up advertisements from time to time you will find that users will just delete the App as I do.
Also the revenue from advertisements is an absolute pittance and unless you have thousands of downloads you are not going to be able to afford that luxury villa in Spain.