I just ran into this on the forum.
I've just started to do instance runs with my move to the Outlands. I've noticed that my trapping technique seems sloppy (I don't always grab aggro, I feel a little slow, etc.). I've also noticed there seems like a significant delay between when the mob becomes trapped and when I turn to DPSing.
So I want to know, after your trap target has been marked, and someone else makes the first pull, what sequence do you follow (with macros, move order, or whatever) to ensure your mob gets trapped and to fairly seemlessly start DPSing with yourself and your pet.
First of all, I assign focus target to my up arrow key. Focus is good to use because it means you can lure your trap target and then commence DPSing Skull smoothly without risk of shooting your trap. You will also want to download a mod which lets you view your focus. Some use Focus Frame, but I use Perl Unit Frames because it does a few other useful things as well.
When you've got it, go into the Player section, turn on player portrait and 3D player portrait, and move the scale down to around 85 or so. Do the same for Party, and then go into Combat Display and set it to Always Hidden. You will want to drag the bars to the right a bit to get your player portrait to fit in the screen; you can right click the Perl Unit Frames minimap icon to unlock them, and then just right click it again to lock them in place once you're happy with it.
Then you want this macro:-
/cast [target=focus] Distracting Shot
Then, as soon as your targets have been marked, (you have to be quick, here) target blue square, (usual trap target) and press the up arrow to set the blue square target as your focus. Then set your target to Skull. Notice that this effectively means that you can have two mobs targeted at once.
As others here have said, move to a good distance to the side of the group if you can and then drop your trap, in order to prevent your trap being broken by someone else's AoE.
As soon as the pull begins, use your Distracting Shot macro to lure your trap target over to the trap. Wait a moment to ensure that the trap target is coming towards you before you begin shooting Skull. Ideally, the single Distracting Shot will be enough, and you can continue shooting Skull. If it isn't enough, try using an aimed or arcane shot with the trap target as your target, but be careful to press Escape twice immediately after the single shot, in order to ensure that you do not break the trap as the mob moves into it.
When the current fight is over, press Escape to clear your target, and then press the up arrow again to clear your focus, ready for the next target.
As far as spec is concerned, if trapping is something you want to focus on to a degree, you may be interested in trying to obtain a few of the midlevel talents in the Survival tree. Trap Mastery is the main one which is desirable, as it reduces mobs' chance of resisting your traps by 10%, and in a number of the higher level 5 mans, that is necessary in order to be able to trap reliably.
I hope this is of some assistance.