I have had some experience writing container-bound scripts, but am totally new to web apps.
How do I debug (e.g. look at variable values, step through code etc) a web app? In a container bound script it was easy, because I could set breakpoints, use the apps script debugger - how do I go about this in a web page e.g. when I execute a doPost?
In his excellent book "Google Script", James Ferreira advocates setting up your own development environment with three browser windows; one for the code, one for the live view (in Publish, Deploy as web app, you are provided with a "latest code" link that will update the live view to the latest save when it is refreshed), and one for a spreadsheet that logs errors (using try/catch wrapped around bits of code you want to keep an eye on).