The Three Sisters companion planting method, which I discovered on the Park Seed Company's web site, is an ancient Native American technique of growing corn, beans, and squash together to increase harvests naturally. Corn acts as a support for climbing bean vines, the beans add nitrogen in the soil for the high feeding requirements of corn and squash, and the squash provides mulch and root protection for the corn and beans.
In May or June when soil has warmed: Shape a flat-topped circular mound of soil about a foot high and 2 feet across at the top, sloping outward toward the base. Plant a circle of corn seeds on top, about 5 or 6, and water them in well, tamping down your soil mound firmly so it doesn't wash away in the first rain. Space the mounds 3 or 4 feet apart in the garden.
About two weeks later: When your corn reaches about 5 or 6 inches high, plant bean seeds (6 to 8 of them) around the edges of the flat top or about halfway down the sloping sides of the circular mound. Push the seeds down deep into the soil and, if you're planting on the slope, make sure the soil is nice and firm. To get your Beans to climb up the cornstalks, choose Pole rather than Bush varieties.
One week or so after that: Plant squash seeds around the base of the mound, on flat ground. You can make them radiate around the mound, or just go in the direction you have available space! 6 to 8 seeds in a ring around the base of the mound is usually plenty.
When everything begins growing . . . Thin the plantings to 2 or 3 cornstalks, each with no more than two bean plants winding around it. (You'll need to help the beans get started growing up the stalks). The squash is going to vine along the ground, so the number of plants you need depends on how far apart your mounds of corn and beans are, how long the vines get, and how much walking space you need in the garden.
Plant other companions like herbs to assist with pest control.