I apologize in advance for my sloppy, longwinded response.
https://forum.nostalrius.org/viewtopic.php?f=24&t=16499While the warrior abilities listed here are for max level, it should give you an understanding of how threat works. Buffing, debuffing, and gaining rage all play a role in keeping aggro.
Keep in mind that buffing and healing does less threat per mob when there's more mobs in the pull. I'm pretty sure it's divided between each mob. So while tanking 6+ mobs at once may seem intimidating, also realise that the healer won't aggro them as fast as say tanking 3 mobs.
Your general abilities to spam will be sunder and revenge. Use battle shout and bloodrage while in combat so they benefit your threat. Save shield block for bosses that hit really hard (the giant boar in rfk and eranikus in st come to mind). In most pulls you won't generate enough rage to spam shield block and keep aggro at the same time. Heroic strike only if you're gonna cap out in rage. This probably won't happen until ST. Cleave is useful for keeping aoe threat but I prefer manually sundering/revenging each add every 15 seconds while using cleave if my rage is getting high. Thunderclap and demo shout are good for getting snap aoe threat at the start. In certain aoe situations it's helpful to spam battle or demo shout. Battleshout works best if it affects everyone in your party and there aren't too many mobs while demo shout will shine if there's an absurd amount of mobs.
I'm leveling as pvp arms so my tanking rotation against multiple mobs kinda looks like this:
(zerker stance) zerker rage, (battle stance) charge, thunderclap, bloodrage, sweeping strikes, (zerker stance) whirlwind, (def stance) demo shout, sunder/revenge primary target for a bit, then sunder/revenge adds so healer doesn't eventually aggro. Sometimes I do a 2nd whirlwind when it's off cd and if I have a ton of rage I'll use cleave. I'll spam shouts if I think it'll be beneficial. If mobs aren't hitting me very hard and my rage generation isn't so good, I'll skip the sweeping strikes step. Damage dealers don't want to wait 5 seconds before starting.
A lot of the times I've been tanking I've used my hard hitting 2hander, using sword n board in bad pulls or against mobs that hit hard. I also execute mobs which means going into battle stnace. You might say that the way I tank is pretty unorthidox but I see it as math (plus I love beating everyone in dps when tanking).
All in all, I say learn how threat works if you don't know already. Once you have that down, just have fun tanking. Don't get all stressed out if ppl aggro, that's why you got 1-3 taunt abilities. It's only until late game dungeons where it'll require more focus. Until then just experiment and see what does and doesn't work.
edit:
It's also helpful to know what other class abilities increase their threat. You're going to run into plenty of shaman and priests that use earthshock and mind blast. There's also not too much you can do other than taunt and scramble if a hunter multishots as soon as you pull. These situations don't freak me out so you shouldn't. You're just around to make sure ppl don't die. If dps aren't allowing you to keep aggro but no one is dying, whatever. Let the healer complain first since it's their mana being wasted.
edit2:
unethical was not the right word. I didn't get much sleep.