Cellphone Anti Tapping: Beware of unknown applications
Know where your apps come from.
Don't just download any app to your phone. While iPhones only run apps from Apple's App Store, which vets all apps sold from the platform, standards are not quite as high on Android.
The Google Play Store has made progress in ensuring its apps aren't running malware, but the Android platform allows installation from various, less-regulated environments.
The best way to avoid malware on Android is to stick with the Google Play Store, unless you are sure you can trust an independent app from somewhere else.