Many gardeners plan their garden out every year, drawing maps on graph paper to design their plots. If you want to increase the size of your garden and don't have a lot of room, don't think of a graph; think in three dimensions. You can increase your garden size dramatically by growing plants vertically instead of taking over a lot more land. Get more planting room by growing up instead of out.
A fence of some type surrounds most suburban back yards. Take advantage of this natural trellis to increase your garden size. Plant cucumbers, peas, green and wax beans, squash and miniature melons in the soil beneath your fence. The plants will grow up the fence, keeping your harvest out of the dirt and leaving the rest of your garden space for other crops.
If you have young children or grandchildren, make a bean tepee in your yard. They'll spend hours playing inside. Tie together six bamboo poles at one end. Stand the poles up in your garden with the tied ends on top. Spread out the other pole ends so that the resulting frame looks like a round tepee shape. Plant four or five pole bean seeds around each pole. The bean plants will grow up the poles as the summer progresses, creating a green living tent for your young ones to use as a hideaway.
Turn a porch or patio into a secluded getaway with a living wall of flowers. Push sticks into the ground at 6-inch intervals all around the patio or porch. Push thumbtacks into the edge of the porch roof with one thumbtack sitting directly above each stick. Tie a length of cotton twine between each thumbtack and its corresponding stick. Plant two morning glory seeds near every other stick. Plant two moonflower seeds around the sticks that don't have morning glories. The vines will grow quickly up the strings, and you will have blossoms morning and night.