I made this Runecloth Farming guide to help out players who want to farm the cloths instead of buying them from the Auction House. I decided to search for places with high density of mobs which I can kill and drop [Runecloth]. I traveled around Azeroth, and after a while I made a list of places.
If your level is not high enough to solo Hellfire Ramparts, killing Twilight Cultists in Silithus is the best place to farm Runecloth. By the time you cycle back to the first camp, all of the mobs will have respawned.
Hellfire Ramparts - instance
The best thing about Ramparts is that once you cleared the instance, you don't have to run all the way back. You can just jump down and go outside. This saves a lot of time and makes this place an excellent farming location. However, you can only do five instance run in an hour, this means if you are clearing this place under 12 minutes, you should go to Blackrock Spire instead.
This is Normal Hellfire Ramparts, not Heroic.
After you cleared the instance, go outside and reset it by right clicking over your own portrait then click the "Reset all instance" button. This restarts the whole instance and all mobs will be back.
Upper and Lower Blackrock Spire
Blackrock Spire is a dungeon at the upper part of Blackrock Mountain. Don't clear the whole place. What you should do is clear the first big room (Hall of Blackhand), and the the next room to the left (Dragonspire Hall). Do not kill Pyroguard Emberseer, just turn back and reset. There are much fewer humanoids at the other part of the instance, and you have to wait like 1-2 minutes at one of the bosses until the event starts and you can finally kill the boss.
Max. level players might clear the instance too fast and they will hit the 10 instance per hour cap. This is why you should head over to Lower Blackrock Spire (LBRS) after you cleared the first two room at Upper Blackrock Spire. Clear everything at LBRS until you reach Mother Smolderweb. Turn back, go outside and reset the instance. Only do this if you can solo the first two room in UBRS under 4 minutes.
Just to make things clear, when you enter the instance, Upper Blackrock Spire is to the left and Lower Blackrock Spire is to the right.
Another great place to farm Runecloth is in Blasted Lands. Drowned Gilnean Merchant and other humanoids around this area drop a decent amount of Runecloth. I must mention that the drop rate compared to Hellfire Ramparts is horrible, if you can solo Ramparts you should go there.
Visit my Netherweave Cloth farming page when you have enough Runecloth.