At lvl 76 Hunters get a spell called Misdirection. Target either your tank or your pet and cast this on them. You then have 30 seconds to shoot a target before the effect wears off. All the threat you cause for 3 seconds will go to the person or pet you put the Misdirection on. You want to use the highest damage shots. You can also shoot Multi Shot and all mobs hit will go after your MD target. If you are attacking a large group of mobs only the ones hit by multi shot will attack your MD target. Any that are outside the range of Multi Shot or a single target shot will come straight for you if the tank doesn't use AoE.
If you make a macro like the one below you can target the person or pet you want to be the target of Misdirection and type /focus. Then you can hit this macro every 30 seconds to bump their threat level up and make their tanking life easier.
/cast [target=focus,exists] Misdirection
This is a Bm talent that can help BM hunters keep argo on their pet. When you hit Intimidation your pet will stun the target for 3 seconds and make the mob pissed off at them instead of you. This is mainly used while soloing but it can be very useful when in groups and a mob is after a caster or healer. The time the mob is stunned or changing argo over to your pet can save the life of a healer or give your tank time to gain argo. Know that you may kill your pet off doing this depending on if your healer will heal your pet or how hard the mob hits.
This is where Hunters play dead. Feign Death is when you fall to the ground and have a high chance of losing all argo. Know that this don't always work though. The fail rate is low but it still happens sometimes. When you see you are getting high on the threat meters FD. You will be able to stand up and start into your shots again as if you never hit the mob before. This is also useful when you are fighting Big Bad Wolf in Kara. If you are turned into Red Riding Hood you can FD for the time your are RRH and the Wolf will go back to the tank. If you get up before then though you will be attacked.
Shadowmeld is a Night Elf racial ability. With 3.0.2 you can use it while in combat. If you get too much argo you can Shadowmeld and get out of combat. When you move or remove Shadowmeld you will have the same amount of threat as when you SMed. Though this does not wipe your threat you can stay hidden until your tank gains enough threat to keep the mob off of you. There is currently a bug between WoWs threat meter and threat meters like Omen. Omen will say you have cleared all threat but you really haven't. Blizz knows about this bug and it is unknown if and when they will fix it.