I find that guard is a very dynamic ability and needs to be switched based on who is taking damage. A good tip is to unguard after combat so you can quickly guard who needs it without using 2 gcd's. Also, it is very important to bladestorm every time it is up to have the shield buff on. Guardian leap and taunts are so important to keep on cd since you also take less damage from guard. We have a boat load of cc. between push, stasis, hilt strike, and awe you can peel for days. Typically when I engage a group of enemies I leap to one target, awe, place guard if I haven't already, freezing force, then challenging call once they come out of mezz, and guardian leap to their focus target... very effective. Furthermore, you can effectively lock out a healer for a very long time. Interrupt, cc, then interrupt again can be all the time you need to drop a target. Lastly, you have a bit of burst with guardian slash and dispatch. If you are assisting you can put a full stack of sunders and help drop targets. Leap, bladestorm, sundering strike, guardian slash, then dispatch is quite a bit of damage. It takes a little bit of practice and gear, but your role is clearly defined and you will become invaluable.