most and the least.  Remember that tomatoes and other tall crops will shade out whatever is growing behind them.  Radishes can be grown in under a month so use spots for them early in the season that you can plant other crops later in the season.  Try planting peas in the back of the garden and put a crop of cucumbers or zucchini in their place in early July. 
I like to leave the front of the garden for my greens and other shorter crops.   Use a piece of paper to plan the garden or you can mark the areas directly in the garden itself.  Remember, plants will grow exponentially during the season, leave space for them to grow.  Crowded plants promote disease and other issues.  In the end, proper spacing will give you a higher yield of your favorite vegetable.