I can tell you that here in new england where i live a simple rectangular 20 x 40 ft.
Dig your own pool by hand.
Check with your pool supplier whether you need to leave room for gravel at the bottom.
If you can make sure you place the pool in an unshaded area and out of the wind it makes a big difference when in use later.
Next mark the area with lime paint or with stakes and string lines.
Tie a string across two stakes 6 inches above the ground level it and measure the depth to the bottom of the hole.
Dig down to a depth approximately equal to the deepest part of the pool.