Congratulations on getting into vegetable gardening. You'll have a lifetime of learning and fun not to mention fresh vegetables.
With 400 sf I'm assuming you want to plant in the ground instead of pots. That being the case I'd start by getting a soil test or purchasing one of the NPK and pH tesk kits at one of the big box stores to determine if you need to add any amendments. Once you do that, decide what you want to grow and take a look at the planting calendar for your county on the county extension web site. I'm new to gardening in the desert but I've found a lot of stuff grows very well here, i.e., zucchini, cherry tomatoes, cowpeas, bush beans, many gourds and squash, and onions. Consider your ability to irrigate as well. With 400 sf you could probably water by hand without any problem. Read as much as you can about building the soil because the quality of the soil ultimately determines what will grow well.

Gene

Contact the U of A Yuma County Cooperative Extension office. They will have tons of horticulture information for your area. Here's a link to planting dates and garden varieties. http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1615.pdf

Here is a link that might be useful: Yuma County horticulture

In addition to the planting calender link AZ1615 provided by aztreelvr, you might link the below link which accompanies the AZ MG Ten Steps Series found in the Yuma MG link also provided.

Additionally if you are a reader:
http://cals.arizona.edu/maricopa/garden/html/pubs/mgpress/mgpress.htm

Here is a link that might be useful: AZ1435

This post was edited by Fascist_Nation on Wed, Apr 23, 14 at 20:53