Welcome to ScreenOS.
Free Material.
Concepts & Examples Guide documentation - The feature set is rich. Skim the table of contents for each volume and determine which features are applicable to your network. Then you can use the sample concepts and examples in these guides to create the configuration on your test unit. You may need other firewalls to create routing or VPN tunnels with for these exercises.
http://www.juniper.net/techpubs/software/screenos/screenos6.2.0/index.html
NetScreen JNCIS-FWV Study Guide (PDF) - unofficial study guide compiled by Jason Ha. He is a network engineer that also prepped for the exam and shares this material.
http://sin.pvs.ro/NetscreenJNCIS-FWV-StudyGuide-v1.3-public.pdf
Paid material but helpful for me
Configuring Juniper Networks NetScreen & SSG Firewalls - If you want a more formal organized introduction, the Syngress introduction to SSG firewalls is really well done. Experienced people can skip the opening chapters that start with even the networking firewall basics but this organizes and introduces the major concepts of ScreenOS configuration and I found it very helpful.
http://www.amazon.com/Configuring-Juniper-Networks-NetScreen-Firewalls/dp/1597491187/ref=sr_1_2?ie=U...
ScreenOS Cookbook - There is also the Oreilly "Cookbook" for the ScreenOS. This is a great reference I use as a first stop for setting up new features. It is a quick and dirty guide to how to perform specific functions. There is not really anything here that is not in the concepts and examples documenation, and that is the place to go when you don't understand or need to modify a configuration presented here, but it is a very convenient short cut for me.
http://www.juniper.net/us/en/training/jnbooks/screenos_ckbk.html
Advanced VPN Implementations Courseware from Juniper. These are the same books and lab guides used for the classes but you take them on your own. You do need to be good at self study. The books are lecture notes. So you have to look up the detail when you don't understand the conepts presented.
http://www.onfulfillment.com/JuniperTrainingPublic/Product.aspx?d=46&p=735&sid=323