Some people will recommend Hurricane to start a pull, this will generate aggro on all of the mobs for a good start. Depending on what CC you have, this may not be a viable option(ie, sap). I usually don't use this method, and have been complimented several times on my tanking in this instance. So, here's my Wall'O'Text response to how I do it.
My strategey:
You'll notice that when you pull the first target usually it'll be in the lead with the others not far behind. I'll usually put maul on, and then mangle as soon as he gets in range. If you're lucky and those crit, you'll have about a 4k threat lead to start you off. By the time the other trailing mobs reach the pack, your GCD should be up, so I'll get ready to implement the next step.
Directly after this, I'll do a demo roar. This is mainly just to keep the mobs off the healer until I can generate more threat. Since the Demo Roar is AoE threat, it'll make sure to get everybody, unlike the other druid talents. Not doing this in the beginning can mean that a healer pulls aggro right away if you get unlucky and a mob gets missed. Losing aggro to a mob in the very beginning makes for a very messy pull because while you're getting the guy off, people will still be dpsing the first target, and probably pull it off of you. Make sure that the dps knows this, even though they probably still won't listen if you tell them.
Next is the swipes. Some people swear by lacerate-tab tanking, but I use a combination. I start with swipes b/c it can crit up to 3 times, which mean extra rage(very nice to have in the beginning of a pull). Before I swipe, if there are more than 3 mobs on me, I'll tab first. This makes sure the one I swipe to is definitely being targeted. I'll tab each one and swipe until I get back through to the main target. Usually The main target will still be hit by a couple of these swipes so that I don't lose aggro. This part is where that Maul+Mangle combo I used earlier comes in handy. It'll generate enough aggro to keep him on me until I tab through for my swipes.
Once I get to the main guy, I immediately hit the mangle and go on to my next step. This one will vary depending on threat that others have. Usually the tabbing will have given them ample time to get pretty close to you on the treat, so I use Lacerate on him for good measure. If the others are not even close to me on threat, I'll opt for "Tab-Tanking", because this will generate extra aggro on the next mobs on the list, which will help once your main target is down.
If the other members are pretty close to you on threat, I'll go for a mix of swipe and lacerate. You'll want to keep the main guy on you(Lacerate), but you'll also want to keep threat on the rest of the mobs(swipes), especially if there is any AoE going on. Remember that the swipe has a conal area of effective so if you turn 45% to the left, you'll get some of the mobs out of the directional range of the ability, thus targeting only the leftmost mobs. If you turn the other direction, you'll get the rightmost mobs. This takes the randomness out of swipes targeting only 3 mobs at once.
The main reason I use swipe tanking instead of tab-tanking if the other members are high on the list is that if the mob gets pulled off of me, I can instantly use Growl to get it back, whereas you'd usually have to select the guy that got pulled off, which takes extra time. Additionally, if the one who pulls it from you is ranged, you'll most likely not have time to growl it before it moves and will have to feral charge to get it off, which will move the whole group of mobs in the process. I find things run a bit smoother when there is minimal movement of mobs going on.
That pretty much sums up what I do for big pulls as feral. It will, of course, vary depending on the group, and this method may not work well for all setups. It's a good start though.