Digging tools, drill, level, bucket, gravel, post (must be rot-resistant wood, rust-resistant metal, or an appropriate synthetic material), 2 x 4 braces, wood stakes, wood screws.
Dig the post hole, making it three times the width of the post and at a depth equal to 1/3 to 1⁄2 of the above-ground length of the post, plus 6" (right). For loose or sandy soil, using a tube form is recommended (left).
Pour 6" of gravel or crushed stone into the bottom of the hole. Compact and level the gravel using a post or 2 x 4.
Set the post in the hole. Attach angled 2 x 4 braces to two adjacent sides of the post using one screw for each brace. Drive a stake into the ground near the lower end of each brace.
Use a level to position the post plumb (perfectly vertical), checking on two adjacent sides with the level, then fasten the braces to the stakes.
Fill the hole with Fast-Setting Concrete up to 3 to 4" below the ground level.
Add the recommended amount of water. After the concrete has set, backfill the hole with soil and/or sod.