The folks at GOA put together an extremely thorough strategy guide for RvR teamplay in Warhammer Online. It covers all the basics from how to form a group to suggesting various ideal career combinations, but it doesn't end there. They're just getting warmed up!
The guide discusses the pros of assigning a group leader and lays out some general guidelines a good leader should follow. It also suggests how a strong group will follow that leader while remaining alert for danger and constantly communicating with each other. Strategic offensive and defensive positioning for various career archetypes is covered in depth. The guide suggests that as important as it is for you to know the roles of you and your allies, it is equally as important to study your enemy and learn their various strengths and weaknesses. Last, but certainly not least, the author runs the reader through various group tactics as complex as you'd find on any whiteboard in an NFL team's locker room!