Crop rotation is extremely important for healthy organic vegetable production. This is a lot easier on a large lot or farm, a small urban garden uses every spare inch to squeeze in plants and rotating the space can be a real challenge! The challenge is greater when you have limited full sun beds. I have found that the key to good crop rotation on a small lot is planning and flexibility.
First, you need to plan for three years. A three year rotation is the minimum that you should rotate for healthy soil and pest management. You also need to plan cover crops to plant in the fall or early spring to feed the soil. Nitrogen fixing crops and those that you can use as green manure are the best options, and when your sunny beds are limited and need to be used for heavy feeders like tomatoes this will help fertility immensely.
Flexibility, or maybe I should say creative thinking, is also important. If you are not afraid to intermix your vegetables with your flowering plants you can gain a lot of flexibility. I have designed my yard for both traditional style vegetable beds and with spaces between other plants for a squash here or a tomato there...