Companion Planting: Companion planting is often touted for the benefit of cutting down on pest infestations. It also serves well to conserve space. Shade tolerant plants will benefit from being planted next to taller crops. Basil likes a respite from hot sun and does well next to tomatoes. Lettuce will keep producing all summer if shaded by almost any taller plant. Early harvested crops, like spinach, radishes and peas, can be planted with slower growing crops like broccoli or peppers, which will take over once the spring crops are gone.
Companion planting is an art and it can be one of the more fun challenges of gardening. Why limit it to the vegetable garden. Mix your vegetables and flowers.
Succession Planting: Succession planting is a great technique for any vegetable garden large or small. But it is all the more valuable when space is limited. Succession planting means reseeding quick growing crops every 2-3 weeks during the growing season. It is especially popular with crops like beans, zucchini and lettuce, that tend to exhaust themselves producing so much. By successively planting, you will have just enough produce for your family's appetite and you'll have it all summer, not all at once.
Crop Rotation: Rotating crops to different areas of the garden each year is an excellent way to cut down on diseases and insect pests that over winter in the soil. This really isn't possible in small vegetable gardens. You'll just have to be vigilant about not letting problems get out of hand. If a large scale problem should occur, such as squash beetles or septoria leaf spot on tomatoes, seriously consider not growing the crop for a year. It will be a sacrifice, but one year without is better than several years of a disappointing crop.