Start the quest named 'Reign of the Black King'
Now make your way through WP Cathedral Garden -> Leorics Passage -> Cathedral Level 2 -> ... -> 3 ->4 and finally to the royal crypts.
Take the waypoint (you'll get the Checkpoint)
and now make your way to the Crypt of the Skeleton King.
Once it loads hit ESC, skip the event, clear the trashmobs before the first gate and leave the game.
Rinse and repeat.
Next game enter normally you won't need to take the way point to the royal crypt because the checkpoint will spawn you behind the ornate door leading too the main tomb.
These trash mobs are called "Returned" they are unique to just outside of Leorics Spawn. Do not kill King Leoric he cannot drop rares as often as these mobs.
Also I am using this to farm rare amulets for my characters.
Added this because I noticed they nerfed others.
Again if you kill King Leoric you will need to re-desend Cathedral -> through crypts down 5 floors of trash mobs. Returned can drop more rares than Leoric can is my understanding from my friend.
Just got Amulet of the Bear, I've also seen a 1-2 damage amulet as well.
I am doing this with 78% magic find.
Can post findings.
They also drop items not found anywhere else in Act 1 (Brigadine coats, rare amulets, uniques, etc)
Amulets acquired: bear, adventurer
at level 11 these runs give 25% of 1 XP bar, so you need to do this 25 times if you want to level from 11 too 12 using this run.
best amulet I have found to date:
http://i.imgur.com/BDcEy.jpgCan post video if needed if your that confused.
I've made several level 13s with this method can post a guide from 1 if your interested.
edit:
The efficiently item whore way to create a character from scratch would be level to leorics tomb and then not taking on Leoric until level 13 with suffient magic find. My understanding is that Leoric will only drop legendary/rares on his first run through then only his 'returned' trash mobs will yield any good items.
I have got the following amulets thus far: % speed increase of attack, magic find, strength, bonus xp, bonus money
Its worth noting that you can give your merc an amulet as well.
edit2: Need a better vid card but can post a video for each class.