Used as sort of an app logo – the app icon’s primary role in app store optimization for Google Play is in conversion.
There are many theories on app icon design, from which colors to use to the use of text vs no text.
Generally, the goal should be to efficiently communicate the app’s main features or otherwise align to them. “Efficient” app icon design in this case means “simple”.
Because of the impact of the App Icon design on app conversion, we we recommend asking potential users, via a focus group or polling an email list.
App icon design tips
Regarding the use of text vs no text in an app icon, icons on Google Play tend to fit into a few buckets:
No text at all
A single letter
A small amount of text – 4 characters or less
Lots of text – a name
Looking at what the market is currently responding can provide guidance as to what approach will work best for an app.
For example, looking at the top ranking free apps in Google Play, 30 of the top 35 use no text or a single letter (like Facebook or Skype).
Google has provided additional app icon design guidelines here.