This works easily if you have high experience in Herbalism, First Aid, Skinning, Leather Working, etc. Get the materials needed for what you want to make. For example, for First Aid, kill lots of humanoids for linen cloth, wool cloth. Then, just sell the materials to an NPC. If you want more money, make something out of the leather, then sell or auction it off at the nearest auction house.

In Ashenvalle, there are Rotting Slime that drop treasure chests with good items.