Many questions and problems that occur while developing RAP applications are not directly related to RAP, but to the technologies it is based on. As an example, layout issues are usually related to SWT, dependencies to third-party libraries are handled on the OSGi level, and questions regarding session handling are related to the servlet container.
Therefore you should have a good understanding of the technologies that your RAP application builds upon. This will likely include Servlet technology, OSGi, the Equinox OSGi implementation, SWT, maybe also RCP. Here are some links to get you started: