Ok here is a guide to swarming: Learned through lots of practice and Dieing!!
1) Find an area with a ton of light blue mobs. Know the mobs: do they summon? do they cause you to fd during a fight? can they stun you for any length of time? can they charm you for any length of time?
2) Find a spot where you can put your back into a corner
3) Buff up: Shaman unity is very helpful, mage ds, enchanter haste. Use cloak with a clicky ds. All your normal buffs: drape, shroud, horror, attack buff, and ds skin if you have it at your level. You will want to shrink yourself. I usually cast an illusion spell for a small race, which is important for when you use visage of death, because vod makes you large if you do not block the illusion somehow.
4)Required aa's: Mortal Coil, Knights return strike, double riposte, theft of life, touch of the cursed, steadfast will, speed of the knight, soul abrasion, spell casting reinforcement, veterans wrath, visage of death, scourge skin, hate step, defensive aa's. Then you will need to work any other offensive aa's so you can burn down mobs quicker.
5) Before each pull I will cast Stubborn Stance, and Sholothian skin(those just starting out will want to try and keep this on as much as possible)
6) Epic 2.0 is needed, Leechcurse will not usually get you to the point of procing a mortal coil. 1.5 will be ok, but will be lots of situtations where you may not get to your mc proc.
7) Good 2 hander, some people will say you can do this with sword and board, I say more power to them, i cannot do 150 plus mobs with sword and board.
Pulling mobs:
Start small, 20 Mobs is a good place to start. As you feel comfortable move onto bigger amounts.
Lots of different ways to do this. Some will cast harm shield and run around aggroing mobs, some will put a non damage weapon in their hadn and run around and aggro mobs. I myself will run around with my main in hand and aggro mobs, about half way through my pull I will cast harmshield, as their are a lot of mobs able to hit me at that point.
Another thing I do is use hate step to get ahead of the mobs by enough where i can cast scourge skin, i will then run around long enough to use hate step again and then get in to my corner, and immediately hit my epic. I keep my face to the wall when casting and then turn to face the mobs. Make sure you keep the back arrow pressed, or you may move forward enough to get a mob behind you and you do not want that.
Once Mobs are on me, I will cast fast DoT's on about 3 or 4 different mobs, and then will concentrate my efforts on a singular mob. Once I have one dead, I will cast visage of death. Once VoD is on you want to make sure you are cycling through mobs. watch to make sure mortal coil procs. If epic is running out and you dont hve mc yet, have leechcurse ready to go, then make sure you burn down a couple of mobs while leechcurse is going, if all else fails FD and start again. RNG can be a bitch sometimes!!
I mentioned this in an earlier post, if you get down to a couple of mobs and still have mc up I would grab some more mobs, and then start killing again, starting with the couple of mobs you brought with you(id say 90% of the time i get another proc with the couple of mobs i brought with me.) if it doesnt proc and mc is wearing off usually epic will be ready again.
Without Visage of Death, you will have to pull smaller swarms. For example: Currently when VoD is active I pull over 150 mobs, when it is not active, I pull around 100. Your results may vary
Feel free to ask me any questions I have swarmed a lot and have died a lot in learning.