You most likely did fine. Things get better once you get jet-charge and are able to be first on the mobs. While leveling, i often had the problem that Marauders would leap at the mobs before i got there, and then spent the rest of the fight trying to peel them off them.
Try to educate your group towards killing mobs from easy low hp > tougher mobs.
IE. normals > silver > golds.
Normal mobs are affected by stuns and such that acompany a lot of player abilities so they wont kill your group if they are taken down first. If you focus on Gold and Silver type mobs while trying to grab a few normals as well you will be fine.
If you get a group where the one DPS goes 'waaahooo' on the Gold star mob, while the other is unloading on the silver mob that is 20m in your back before you even got a chance to hit the mob once, there really isn't much you can do, except taunt and hope the mob is dead before it runs back to DPS #2.
Talk to them or try find a better group. We are tanks, not miracle workers
Open with Death from Above whenever it is available unless you know that a certain pull will spawn additional adds after you engage and there is no clicky bomb around to help you grab the extra adds.
Most groups generally move quite quickly through trash so Death from Above will not always be available. Later on you can alternate with jet-charge > carbonize > flame sweep or flamethrower and use grapple to pull in that loose end add that is standing a bit off to the side.