1. Don't overcrowd the shot
Don't try and capture too much in a single image, especially if it's going to be cropped and uploaded to Instagram anyway. Focus on a key area, such as the sheen of an egg yolk1 or a steak's pink centre, but not so closely a viewer won't be able to tell what it is.
2. Consider the lighting
Using a flash in a dim restaurant will bleach2 your food of any defining features and splashes of colour. A plate will always look better in natural light, but when sunshine is out of the question, make sure you're focused on using as much of the available light as possible, or try and use the shadow to your advantage.
3. Keep it steady