Our guild hall has now got a rank 2 arena. This means that we've unlocked the ability to use it, basically. This can be done by going to the Coliseum Waypoint (bottom right) in the Guild Hall, and selected either the red or blue team.
This will be how we organize tournaments. It's also a good way to practice with other guild members that aren't yet ready to enter the Heart of the Mists.
Plus it's fun.