The importance of good nutrition for your dog is often times overlooked, but spending an extra bill for quality dog food will usually save you a big vet bill in the future, and increase your dogs life. The hard question to answer: what is the best food for my dog? unfortunately there is no one answer to this because it all depends on you and your dog. If your dog has health problems or allergies he will need a more specific diet.
But, there are some general things to look for in dog foods, and many dog foods to stay away from. One of the most common issues with dog food is that most low quality, cheaper chows are corn-based. This means your dog is getting enough calories, but is undernourished. A good quality pet food will be meat based, and will not have corn listed as a first ingredient, if at all.
A few other ingredients to stay away from are artificial colorings and flavorings, meat byproducts, any corn product or corn byproduct, gluten, grain-based and countless others.
Here is an example of a good dog food and a bad dog food. The dog food on the right (Purina) is a great example of a type of dog food you want to stay away from.
And another example of a bad dog food:
As you can see, the first ingredient in both of these foods are corn, which is very hard to digest for your dog and low in nutrition. These foods are basically full of fillers, with all sorts of added chemicals like colors, and things your dog does not need in its diet, like sugar.
I usually like to get dog foods with at least the first three ingredients a meat source. But some dogs can have allergies to meats, so other protein sources may work better for your dog. It all depends.
Here is a link that is extremely helpful with comparing different brands of dog foods. It shows you ingredients, and highlights the good and bad things about the food in a clear, understandable format.
Another option that I won't go into much detail is a raw diet. This is when you buy your meats and supplements and make your dogs food yourself. This method is very expensive and time consuming, and is definitely not for everyone, but is generally a healthier alternative to dry dog food.
If you know your dog's specific needs, and learn how to read and decipher dog food labels, you can make an educated decision on which food is best for your dog.