Add the sugar, flour, cocoa, and salt to the mug and mix. Then add the oil and water and mix the dry and wet ingredients together. Be sure to be thorough, there's a tendency for clumps of the dry ingredients to form
Microwave on high for roughly a minute. You may have to microwave it longer or shorter, depending on your microwave, but the brownie should still be wet in the center when done.
http://www.instructables.com/id/Mug-Brownie/?ALLSTEPS