Measure out the area for the deck's foundation and mark the corners with stakes. Place footings at each corner and measure the distance between the footings and the diagonals. The diagonal distances should be equal in order to have a square deck.
Position the center footing and place a 2-foot by 6-foot board across the first row of footings. Use the level to ensure the joists are level. If necessary, add or remove soil until the boards are level.
Position the remaining footings so they are equally spaced and aligned in three rows. Continue to position the 2-foot by 6-foot joist boards in parallel rows in all the joists, checking that each board is level.
Line up the front and back rim joists so that they are aligned with the side joists and screw in place with deck screws.
Cut six sleeper pieces to be placed in between the front and back joists and the rim joists. Position the sleepers in between the first joist and the rim joist at each of the footing locations.
Verify the straightness of the deck frame by measuring the diagonals and adjusting as needed until it is square.
Install the decking boards by placing the perpendicular to the joists. Drive two screws into the boards at each joist and leave approximately 1/8-inch between each board.