Recently, i am working on a small project for producing a mobile web application using GWT. I have read lots of advises and subjects about this, there are several third party library (like mgwt, and ...) which can do this but for right to left considerations i would like to use pure GWT. After several days i find some useful tips:
  • Use MVP pattern for building Device-specific UIs.
  • Use formfactor property in Deferred binding or FormFactor module to select best UI for client device (tablets, phones and ..).
  • Use DockLayoutPanel as much as possible for better layouting.
  • Capture and respond to device orientation changes using ResizeHandlers.
  • Use GWT's Client Bundle to batch resource fetches for increase responsiveness.
  • Use Code Splitting to grab only the code you need to minimize startup time.
  • Use Application Cache (HTML5 feature) for Loading resources like HTML, CSS, and JS from disk.
  • Use HTML5 local storage feature for working without connection and reading/writing data into local database.
You can get this pdf and also see this link to see several useful tips, there is also a good chapter in this book about building mobile application using GWT.

Have a nice time.