Say what you do (yes, really).
Do what you say.
In an academic study published last year, researchers created a tool that analyzed the language used in the privacy policies of 11,430 Play Store apps. They found that 14.2% (1,618 apps) contained a privacy policy with logical contradicting statements about data collection.
Examples include privacy policies that stated in one section that they do not collect personal data, only to contradict themselves in subsequent sections, where they state they collect emails or customer names, which are clearly personally-identifiable information.
Self-contradictions can lead to the identification of deceptive statements, which are enforceable by the FTC and the DPAs (data protection authorities) of the EU.
Details from ZDNet.