Put on your safety gear. Power equipment can throw debris that could blind if it comes in contact with an unprotected eye.
Stake off the four corners of the shed and add an additional 2-foot perimeter within the staked area.
Remove the sod from within the staked area. This can be done with a shovel, sod cutter or a rototiller. Remove any rocks or root.
Check the levelness of the pad in several locations, including the perimeter and diagonals. Use a piece of 2x lumber that is straight with a 4-foot level sitting on the narrow side. Remove any high spots with a shovel.