Draw the outline of your pool on the ground with a piece of chalk.
Stick a stake into the ground in the middle of the outlined area.
Extend a board from the pool's perimeter to the stake.
Set a level on top of the board.
Loosen the grass and dirt from the higher areas with a shovel. Use a sod cutter to remove tough pieces of grass. Remove the ground from the higher areas to line up with the lower areas.
Move the board and level to the next spot around the perimeter once you've completely leveled one spot.
Shovel and dispose of the grass and dirt around the entire pool area until each area shows as level when the board and level are set on that spot.