One question I get quite often is how to setup a development environment.  Another question I commonly get is how to use gProject.  gProject is a panel that allows you to easily create a project, manage your library and most importantly allows you to very easily create custom Classes in custom packages.  Further it allows you to auto import UI (User Interface) objects into your custom built Classes.  If you don't yet have it I strongly suggest you stop this tutorial and go and get it.  It WILL make your life much easier.  You can get it here:  http://www.gskinner.com/products/gProject/about.php

In this tutorial I am going to show you how to:
1. Create the development directory structure;
2. Set up your deployment settings;
3. Set up a Classpath:
4. Create a Main MovieClip and create a Class for that clip that is stored in a custom package;
5. Create a TestObject MovieClip and create a custom Class for it;
6. Import that new UI TestObject into your Main Class and then do something to it (simply change it's alpha to 50%).

If you need help on setting up gProject you can get that from the site above.