I'm no expert on food photography, but I have learn a lot of tips from blogs in the past year. The biggest helper in improving my cookie photos was building two lightboxes, which I wrote a DIY post about on my blog. I know nothing beats natural sunlight. However, I work full time and can only take pictures in the evening. These lightboxes are a huge help at night.
The other aspect of better food photography is staging and composition. I got great tips from the e-book, Tasty Food Photography. She walks you through the correct way of composing a shot, the right settings to have on your camera, and also how to edit your final photos in Photoshop and/or Lightroom. I know there are a lot of free resources for tips on taking better photos, but I didn't "get it" until I read this e-book.
Here's my blog if you like to see my photos: www.semisweetdesigns.com You can really see my photo-taking progression when you compare my very early blog posts to the more recent ones. I hope this helps.