Agreed about location as the #1 most important thing. For example if you're in a high demand tourist area then you can fake it and still succeed. I know of a stay that's a block from the beach, has really poor reviews and it's in a dingy area actually.... always booked during the summer!
I won't name any less desirable cities, but there's some areas where it's just not worth doing Airbnb unless you like working for peanuts.
The rest is not rocket science. Spend some money remodeling the room and buying some nice furniture, bedding, etc. Take pictures with the room well lit. Using a $100 Canon PowerShot + a little color correcting and that will suffice for pictures. After that it's about cleanliness, including making sure the room has no smell.
