As we mentioned already, the Brawler's Guild is one of the more fun things to come with Mists of Pandaria, let alone patch 5.1, so if you're lucky enough to be in one already, why are you reading this anyway, go brawl!
As for the rest of us waiting on that invitation, Wowhead have thrown up a guide for the guild and detailed all the aspects of it.
There are 36 bosses to kill and 8 ranks to climb, with the bosses getting progressively harder as you come up in the guild. There are also special guild consumables and other vendor items, but I'll let you check all that out on Wowhead's excellent guide page:
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