Push your tiller blades about 6 inches into the soil, pushing it slowly up and down your garden plot until the soil is loose and crumbly. About 5 ½ feet square should be plenty for a small plot.
Amend the soil with about 3 inches of mature compost. Till the compost under the soil. Corn needs plenty of food, especially in the first year. Beans won't provide nitrogen until the following year.
Draw a grid in the soil showing 18 inch square sections. Mound the soil up into flat-topped mountains in every other grid square. Push four corn seeds into the top of each mound, spacing them about 6 inches apart.
Water the corn with about a pint of water every three days for each mound. Wait until the corn grows about 3 inches high. This provides a trellis for your beans.
Push three bean seeds into each corn mound about 3 inches apart from each other and the base of the corn plants. Water with about a pint of water per mound.
Push a triangle of squash seeds in each space between the corn mounds. Space the squash seeds about 4 inches apart in a triangle. Water well with about a pint of water per mound.
Wait until the beans reach about 3 inches long. Train them toward the corn so they begin to twine around it when they get larger.