We take all of our own food photographs, and people often comment on them. I am certainly not a trained photographer, but after hundreds of food photographs, I've learned a few tricks.
Sunlight is good lighting for food photos. Indirect sunlight is usually best (although direct sunlight will work in some instances, like the photo above). Our kitchen table is near a window, and I take most of my food photos with the plate on the table, close to the window (curtain open). NO FLASH, just sunlight.
Use your camera's macro setting. Get really close to your food. Yum!
Watch out for background objects that look pretty but are distracting. These stainless steel cannisters really distract from the beautiful lunchmeat being displayed!
Garnish plain foods if possible. This chicken looked really pale and plain. I didn't have much on hand, but just sprinkling some black pepper and dried parsley flakes added a little extra color.
Flashes should be used as a last resort, in general. The washed-out look, sharp shadows, and off-color is difficult to edit out of a photo. If I absolutely must use a flash (i.e. I was cooking at night instead of during the day!) the trick is to stand back and zoom in on your food. Since you're standing back, the flash isn't quite so harsh. Sunlight is still better though!
Fill the plate and arrange it attractively. This is a beautiful plate of food, but it wasn't close to the window. It was taken too far back, so the food is fuzzy and the colors are off.
Don't take a picture of leftovers. This food is delicious served hot. I ate instead of taking a picture. The leftovers looked cold and gross. To top it all off, it was dark outside by then, and I had to use a flash, indoors. YUCK!!
Use a plain plate/bowl/background, unless the design adds to the display. These quesadillas look delicious, but the design on the plate distracts.
Photos looking straight down at a plate aren't usually as nice as angled photos. This photo was taken with a flash. The setting looked great in person, but the picture turned out awful!
These are just my basic tips about what works for me... I have many many more photos I could use for examples, but these will hopefully give you a good enough idea of what I mean. I take about 20-40 pictures of each food. I cringe when I see some of the pictures we put on this website when we first started it. :D