This one is super important for any Android developer.
Apple used to be the only network who was strict about the rules. Not anymore.

So, if you don't want your apps banned from Google Play, follow these rules:

  1. Do not include User Reviews in your app description
  2. Do not use names of other apps in your description or review replies unless context demands it
  3. Do not ask user’s to revise their ratings, by any means (not even emails)
  4. Do not spam other apps by posting your app links in their reviews
  5. Do not incentivize user to enhance their rating by any means possible
  6. Do not repeat or overuse keywords in the description
  7. Do not use unrelated keywords in the description
  8. Do not put someone else’s content without permission inside your App
  9. Do not trigger an SMS / email from inside your App without showing the content to the user
  10. Do not use sexually explicit or erotic content. If used, rate it appropriately according to Google’s content rating policy
  11. Include Ad disclosure in your EULA if you are showing advertisements in your App
  12. Dot not place Ads in notifications
  13. Do not use deceptive ads to promote your app, stop your ad partners from doing it too
  14. Do not use 3rd party payments for In-App purchases of virtual goods (Use Google Play’s in app billing for it)
  15. Use 3rd party payments only for the physical goods or services outside the phone
  16. Avoid copyright infringements, impersonation or any trademark usage in your App, Images or description
  17. Do not generate premium SMS from your App
  18. Do not use system based icons or any other system based UI impersonation in your App

Full article, with screenshots and explanations - here:
http://www.openxcell.com/18-mistakes-avoid-getting-app-banned-google