Here explain how it works fury: clicky
How to keep the bar filled, u can earn fury either attacking or being attacked...
So for brutes, to herd make them stronger, since the enemies will be attacking him.
Also to attack continously will fill his bar, so u should go for a fast activating low end attack chain to fill up ur fury... Tipically, think in put on auto brawl, with an end reduction on it (u can slot brawl, although it will not do much)...
Hope it helped.
Cheers.
Fury is always active, though an empty bar doesn't do anything.
Fury can go from 0 to 100. Each point of Fury increases your base damage by 2%. A full Fury bar, in theory, would increase your base damage by 200%.
However, fury decays at an increasing rate the higher it gets. Therefore, a full bar of Fury is rarely if ever seen. Typically, when soloing with a decent attack chain you'll cap at ~85 Fury. Still, that's only 30% of a damage boost you're missing, so you should still tear things up quite nicely.
IF I recall correctly, you gain 4 Fury per attack YOU perform, and 2 Fury per attack directed at you by enemies. Taunt is useful in teams to keep mobs on you, so you can gain and keep Fury efficiently.
Maintaining Fury can get you into a rush mentality, but do consider your teammates and your endurance bar. An empty Fury bar is still better than an empty Health bar.
If you're soloing and trust your survivability against a single mob and need a quick AFK but don't want to lose your fury a neat trick is to make sure you have brawl set to automatic, leave one mob, and just autohit him while you go afk for a minute or two. Your fury bar should be pretty full when you come back. 
Hi,
I have just recently come back to COX after a long break and have made myself a Duel Blades/Fire brute. One question, though is how do i make my fury go up and what does it do, for instance does it only work when full and is there a power i should use to activate it like domination. Sorry for such noob questions but i found last night that my fury wouldnt even go over the 1/4 mark.
Thank you.
P.S i hope its called fury i just saw someone mention fury on these baords yesterday.