The document provides 8 rules for building a web application effectively on Google App Engine: 1) Design a simple data model, 2) Handle data model updates via a non-default version, 3) Use techniques like Appstats and caching to reduce costs, 4) Improve cold startup times by minimizing dependencies, 5) Use Google Guice as a dependency injection framework, 6) Leverage GWT for performance, 7) Adopt the GWT MVP pattern for large apps, and 8) Consider frameworks like Apache Wicket that are optimized for App Engine.