Step 2: Detangle the hair
Take a before-picture or your friends will never believe you when you try to describe what the doll used to look like! (Many preferably.)
There are two methods to go about the first (actual) step, below, I opted to do a dry detangle which I've found works best for a very matted or incredibly long hair. What you will need the most here is patience! First, only using your fingers, make as much "sense" out of the hair as you can, finding "where everything belongs" by sorting out strands and possible dread locks and full knots. Take out every foreign object you can find - like in the dark haired dolls case a pin and cable ties. (Yes, seriously.) When you're gone as far as you can, take the metal comb and start combing from the ends toward the top - as you would your own hair. No matter how careful you are, you will probably loose some hair - the more dolls you restore this way, the better you become at saving hair.
You can also try using a detangling spray for dogs during this step, or hair conditioner and water. If you have detangling spray, you should use it, but you might not want to spend 6 hours in the bathroom like this sort of mess sometimes requires!
Don't try to solve the whole mass of hair at a time, but take portions until you've got the whole head done.
After this, you may have a detangled hair, but it still doesn't look very good, does it? Now, let's tame that thing.