I will tell u all u need to know about proving grounds.
Proving grounds is a mix of brawlers guilds and challenge modes. You get put into a solo scenario where ur gear is scaled down to 463 and you need to overcome mobs in a different set of waves. I'll be covering only the DPS section as I havent tried the healer/tonk yet.
Slayers: They do nothing, just attack and kill them. They are merely a obstacle.
Oracles: They heal a lot. Make sure to kill them first and interupt them. I recommend getting tidyplates and mouseover macros for your interupts so its easier to keep track of their casts if you're fighting other mobs.
Monkeys: They run quickly and throw bananas at you. They have a ring around them which you need to stay inside of or you will miss a lot of your attacks.
Defenders: They have a 4 sec cast which spawns a deflecting barrier in front of them. You want to get behind them or interupt the cast with a stun.
Amber shapers: These mobs are very important and I like to save them for last before finishing them off. They cast a ball of amber that stuns you if you get hit, the stun is 5 seconds. However, you are supposed to kite them into other mobs to stun them and they will take 50% more dmg for 5 sec.
Sha: Sha's are stationary big mobs with tons of HP. They have a shield on them reducing damage taken by 50%, but after a short time they will be vunerable and you need to pop cds to take them down. Sha's often appear on end of a medal run (wave 10 out of 10 for example)
Virmen: These ones spawn in a massive pack. They are like the slayers, they do nothing. Just aoe them down.
Banshees: I saved the most important for last. The banshee. When it spawn, it will blow up after 8 seconds. If you do not react fast and switch to this, you will die.
You want to kill monkeys and oracles first. They are very annoying to be kept up with the exception if the banshee. Banshees are 100% top prio and must die. Defender and amber shapers can be left for last as they are easily countered by movement only.
Some macros you wanna use is mouseover macros. As a warlock I'm using mouseover optical blast and gateway from 9'oclock to 3'oclock looking at the area from where you enter with a portal to the middle so its easier to kite the orbs and intercept monkies.
I want healers and tanks to write too what they feel is neccesary so we can fill this post in for people who seek help with proving grounds. I will edit it.