There is no one correct way to photograph food. Depending on the purpose of the shot, you have myriad ways to approach how you will take the photograph. A shot to illustrate a step in a recipe will be taken in a much different manner than one destined for your kitchen's wall. You need to have a vision of what you visually want to convey. You need to be focused totally on your photo, but your photo need not be totally in focus.
If your photo is not for how to or documentary purposes, using selective focus may result in a more successful image. It can be used to highlight one part of a dish or to eliminate a distracting background. Often, the results are dramatic.
Here is an image where I strived to have everything in focus:
Not the most compelling of photos seen here in Sautoir Land.
Here is the same image using selective focus:
I find the second image much more interesting.
This is all great you may ask, but how can I do it? Glad you asked dear reader. All SLR's will be capable of doing it as well as many point and shoots. It requires you to take your camera off the fully automatic mode and move it to what is called aperture priority(It can be done in manual of course, but this is the easiest way to obtain it). You will have to consult your manual on how to do it on your specific camera, but most cameras will have a control dial on top. This dial is where you have the different modes your camera can shoot in, marked by cryptic glyphs. You will turn this dial to Av on Canon cameras. Most other makers will have this mode marked with an A. This mode allows you to set the aperture on the camera while the camera sets the shutter speed. If your eyes started to glaze over, just stick with me. I will spare you the camera geek speak and just set you up to take photos.
You now have to decide how much of your dish you want in focus. If you want a lot of your dish in focus, dial in a large aperture number. How you adjust aperture varies by camera and lens. Setting the aperture to f8 or f11 will have your entire plate pretty much in focus. Dialing in a small aperture, like f2, will have much less of you dish in focus. If the part of your dish that you want in focus is not in the center of your frame, here is what you have to do. This technique should work on most cameras. Aim at what you want in focus and press the shutter half way down. You should get some audible confirmation of focus. Holding the button halfway down, compose the photo you want to take. When you have the shot set up to your artistic ideal, press the shutter button the rest of the way. What you wanted in focus should be in focus and the rest should be artfully blurry.
Keep practicing until you get the desired effect. Go ahead and play with the aperture setting as well. In fact, you should play with all the wonderful things your camera can do. Hey, you paid for those features. Most important of all, have fun. If you don't like what you see, just delete it. Remember the number 1 secret of great photographers is to only show other people great photos.