Pretty simple really to do this, you just need a bit of time for your first trap to cooldown. It is accomplished by pulling one mob into a pre-placed trap, and then immediately placing a second trap and aggroing a second mob into it. There are specific situations where this could be useful but they are extremely limited and I cannot, in truth, think of any off the top of my head, where it would be preferable to have 2 mobs CCed for 20 seconds vs. having 1 mob CCed for a couple minutes.

Trapping caster/ranged damage dealing mobs

This can be a little tricksy to be honest. If the mob is a caster type, it's not so bad to do. You just aggro the mob and then either run back out of its range towards your trap, way in the back, or run around a corner or somesuch and break its line of sight on you. In either case, you need to have your trap placed so that it is DEFINITELY in the mob's path it will take to you. This may take a bit of time depending on the situation though and you can also use Silencing Shot (if you have 41 talent points in the marksman tree) to help get that mob moving. Often times a caster type mob will stand still as soon as it breaks out of your first trap and not move into the second one, but instead, start casting on you or a heal on its buddy or whatever. Silencing shot and/or scatter shot are pure <3 in this situation - though you need to be aware of the possibility of following up your Silencing Shot with an autoshot which may break the mob out of the trap it's going to step into as it tries to run towards you, finding it cannot cast.

There are some "hunter" type mobs as well that are a real pain in the butt to trap, since they will just start pewpewing another target if they can't get LOS or range on you very often. I am thinking of the mobs in Shattered Halls for example. These bastids also have scattershot which is pleasant. For them you can do a few things. You can scattershot them in the face (or intimidation) and walk up and place a trap at their feet - though this will limit your ability to chain trap them, or you can just wait til they're shooting someone else (hopefully not scatter shooting your tank in the face though) and drop a trap at their feet... orrrrr you can be really leet and hump their dead zone and get them to follow you quite often. Aggro the heck out of them with your trap nearby, move towards them to the point that neither of you can shoot each other (in both of your dead zones) and you may eat a scattershot, but better you than the tank, move up forward and smack them with a raptor strike or the like and back up... trying to stay in their dead zone as they will follow you at that point, defaulting to trying to melee you before waiting for you to clear out to shooting distance. This way you can step-by-step kite them into your trap. This will likely not work well in a heroic instance though since they may very well just hit too fargin hard and you will have a hard time staying in their dead zone and staying alive. So yeah... tricksy, do your best, and if you must, just scatter them in the face and drop a trap at their feet and if you don't have gear or talents to reduce trap cooldowns, just accept that they will be shooting you or someone else for a few seconds between traps.