Rarely do you fight a group on one mob. Even boss mobs are groups of mobs against groups of players. The jobs are setup specifically for this (being able to take some amount of damage). However, you still want to keep the amount of dmg your mages take to a minimum. Also, hybrid classes are meant to be able to help heal and help tank, sometimes at the same time. Let your pally or shaman or druid take that add sometimes ^^ However, usually, as War, you will have 2, 3, 5 mobs on you at once. That is 'as intended'
Taunt - Only available in def. stance. Sets the amount of hate a monster has toward you equal+1 to the amount of hate it has for it's current target. This means you do not spam it and once you hit the taunt you need to smack that monster some more to get more hate. (this seems weird coming from some other MMORGS, but it does allow tank-switching in instance/raid encounters. With one taunt a different warrior can absorb ALL the hate someone else has been building for the last couple minutes and take over).
AoE Hate - you need to try and use some AoE hate to try and hold more monsters on you, the more monsters the more rage, the more rage the more hate. Use demoralizing shout and thunder clap. I also use dynamite to help with that. Also use things like cleave when you get it.
Switch Targets - Usually you need to switch targets often and hit them with things like sunder armor to get some more hate up.
Warning on HS: This ability (adds damage to next swing) causes your next swing to not generate rage. Careful about spamming yourself into having no rage, that could be trouble.
Sunder Armor - Good hate grabber cause it does not need to wait till your next weapon swing.