#7. Know How to Use Depth of Field

Know what depth of field (DOF) is (and isn’t). This kind of goes along with tip #3. If you want your photos to look professional, you need to know how to control foreground and background blurring (Bokeh). Adding too much blur, in other words leaving key elements out of focus, is for amateurs! Control what your images reveal to guide your viewer's eye to what you want them to see.
Check out this meatloaf photo . It's hard to know where the photographer wants us to look. The lighting is okay, but nothing is really in focus here except one little spot of red in the middle. It's a cool composition but poorly executed because the depth of field 

Meatloaf. Courtesy of Yelp.

(AKA depth of focus) is off. I want to see the front of this meatloaf. It's got great texture and flecks of color but it's blurred out. This is probably the second most frequent mistake I see with white balance problems  (Tip#5) being the first. Depth of field is an important artistic decision. Learn how to use it! That means learn to use your aperture settings!

It would have been easy to blur out part of this dish including the food at the back of the plate if the settings weren't right. Everything on this plate matters and needs to be in focus to tell the whole story of the dish.