Here's a little guide I made one night when I was bored
Here's the starting point, you jump up there and start walking along the rope, keep a bit to the left as you start coming near the wooden thingy, in the beginning I always fell down because I went too far to the right.
A tip: using the button that makes you WALK slowly instead of running might help here!
When you get to this point, do a jump+tap forward key, for a short jump so you get up on the wooden thingy. Once there, face upwards and walk along the wood thingy until you get to the bump (next image)
Here's the place you're supposed to stand, you can stand a bit further, but it might be risky sometimes!
Find a target and start shooting your stuff
See, they don't attack me ^^
Free HK's to the people!
Here's a little thing I made to make you see the range, this is a flamestrike (36 yrds) at it's maximum range from the recommended position, and as you can see, fireball and pyroblast has longer range, so you can shoot everyone that is pretty much anywhere on the "pavement".
Things worth mentioning:
You don't have to be fire to do this, frost is awesome aswell but I was playing around with a moonkin druid and respecced just to have some good overall damage, you can use your water elemental to burst people down aswell, but watch out so that it doesn't come in range of the guards. The guards have strange aggro mechanics sometimes.
Another thing: Guards can sometimes spawn underneath the thing you're standing on (can't remember what it's called, english is not my first language.) Then it's better to just abandon the place for a while until they despawn.
The build I was using for this was Talent Calculator - World of Warcraft but you can really use anything tbh.. (The flamestrike thing is just for fun when there's loads of allies somewhere. PoM + Trinket + Flamestrike + Blastwave ftw
Hope you can have as much fun as I did, and GL with the ganking/HK farming!