If you have access to one, a pressure washer is the best deal.

I use Najaho wool blankets. What I do is soak them in a tub of water with dish detergent. The longer you let them soak the easier the job is but if its winter you only need to let them soak for 5 minutes.

Then I lay them on the dog kennel and put more dish soap on them and brush them with a stiff brush. I use a gunsmithing extra soft wire brush that is so soft you could brush your skin with it but a regular brush like you would use for scrubbing floors would work just as well. I used to use an old fashioned scrub board but I find brushes work faster. Then I hang them on a fence and hose them off with a regular garden hose to get all the soap out of them.