Lets start with skillz
http://eu.battle.net/d3/en/calculator/barbarian#bQUkiP!ZYe!bZZcYcPassiveRuthless - This skill will increase your damage massively. The whole build revolves around getting as many critical strikes per second as possible.
Weapon master - Use an axe with high damage (I use 800 damage) increased critical strike damage and life on hit. Both critical damage and life on hit are very important. An open socket is also very useful because you can add an emerald to increase critical strike damage or amethyst for more life on hit
Superstition - This skill is very useful. It reduces ranged and elemental damage and by 20% and has a chance to gain 3 fury when you take elemental damage which is brilliant when fighting molten/arcane/desecrater elites.
Active Cleave -
Scattering blast - This is your main fury generator. You will buff yourself before hitting enemies using War cry, Battle rage and Overpower so each strike has a chance to fill your fury to max if there are enough enemies in front of you. A critical strike will send enemies flying back and knock them into other enemies which can cause another critical strike and then push them back causing a ripple effect. The knockback also interrupts big damage attacks such as the fallens giant leap attack.
Overpower -
Killing spree - This does a nice chunk of damage to enemies around you and increases your chance to critical strike for 6 seconds. The cooldown can be reduced by landing a critical strike so it's very spammable and costs no fury so it's free damage!
Sprint -
Run like hell - This may not seem like it does much but it's a brilliant way of keep your fury and health up while also dodging nasty high damage attacks. The nados stack quite a bit if you have a fast run speed and keep spamming it so it does enough damage to take down bosses by using this alone. I've killed the butcher/Mahgda and Zultan with this by just running around him in circles and dropping overpowered whenever it's available. Every hit heals you by your life on hit so if you have 3 hitting ever second you heal very quickly.
War cry -
Impunity - This is essential because two of your passives are taken to increase your critical strike so you can't use tough as nails. The boost in resistances really helps to reduce the amount of damage you take from elemental damage.
Battle rage -
Into the fray - This gives you a small boost to your critical strike and increases damage by 15% which is decent but the main use is for the chance to gain 15 fury for every critical hit. You should have this active ALL THE TIME!
Wrath of the berserker -
Thrive on chaos - This is a brilliant skill. It gives you a massive boost to attack speed/critical strike/dodge and also makes you immune to jailer/freeze/vorpal/fear and other control impairing skills. You will need to use this against all elites. If you keep this up with battle rage and sprint a few tornadoes every few seconds you will gain enough fury to keep it going for the whole fight. You have to keep an eye on the timer for this skill and make sure that it never drops below half because occasionally you will be unlucky and your critical strikes wont generate any fury and you'll find yourself frozen or jailed and dead.
GearYou want to focus on getting your vita and strength up. 1000 for each will keep you going through inferno (I currently have 1000 strength and 800 vita) and 600+ resistances before war cry is important from act 2 onwards.
Boosting critical strike helps a lot. Your skills alone give you 38% chance and 50% extra damage. Try get critical strike to 50% + with all your skills active so even a measly 12% from gear is enough to keep wrath up through a whole fight.
More critical strike damage - As much as possible. Mine is at 228% and my cleave critical strikes for 40k damage while overpower does 50k. My damage with buffs is 19k. Tornadoes strike for 8-9 k and cleaves ripple does the same at critical strike.
Life on hit. The more of this the better. If you can get 800+ that would be ideal (you can get this on a weapon alone) I only have 700 and am almost at Belial with very few problems.
Life per second. Not as useful as life on hit because you can land more than one hit per second making 800 life on hit much more useful than 800 life per second. Still it's useful for those occasions where you have to kite but if you use sprint while you're running then mobs will run through them granting you more life!