It has taken 2 years to get it like that, but basically the weather really helps (it is never below the 30's)
We have a large heap-- about 3' x 6' and 3 feet tall, and we let the chickens dig in it all day so they are consistently turning it and their dropping help heat it up as do the grass clippings from all of the nitrogen.
If you are in a cold place I guess covering it with a black tarp would help increase the heat, and a PVC pipe with some holes in the sides for ventilation would be good also, we don't turn it often which helps the heat and you have to make sure that it doesn't get to dry. But the chickens are the main part, it has to be big enough that the chickens can dig it up and chop the food and poop on.
There is a good description in Mini Farming: Self-Sufficiency on 1/4 Acre, that is a great book and I suggest getting it.