We did the Guild Rush for the first time today. Despite a lot of trouble with connections, we managed it. I’ve no idea if the trouble was related to the guild rush or not at the time of writing.
Dulfy has another great guide for this. There is one other thing I can say that should help you.
You need to take your time. Make sure your health is high, stop and regen out of combat. Use all of your buttons especially 1 which finds traps. Wait for it to come off cooldown. Don’t run into a group of mobs. Wait for escorts. The run we did (Bear) took only a few minutes to complete if you survived so there is plenty of time for escorts to help the first wave who can then return the favour.
On another note, it seems anyone can start the 30 minute timer so wait until the guild is ready before you click. Also, you can complete after the 30 minute timer for the individual reward, just not the guild and extra rewards.