1) Puppies need puppy food.
No, they really don't. If you have your dog on a high-quality diet, it's actually better for them to go on an all-life-stages or adult diet.
Why? Because the whole philosophy behind puppy food is flawed. Puppy food is there to "support" fast growth. It has higher levels of protein and fat that help a puppy grow faster and put on weight better.
But puppies don't NEED to grow faster. They're not cows, being fattened for market. They need to grow SLOWER. Slow, even growth and a later maturity is much, much better for dogs, as has been shown in multiple nutrition trials. It's especially good for joints and to prevent dysplasia and arthritis if a puppy is kept thin and grows slow and light.
Puppies need to eat enough to keep their blood sugar stable, so you need to be sensible and make sure they don't go with empty stomachs for a long time, but they will do better over the long term on a food that gets them to adult size at 18 months, not nine months.
2) It's bad to switch foods or mix them.
Nonsense. If you want to keep seventeen bags on your counter and feed some from each bag, go for it.
What causes stomach upsets is when the dog has been fed the same thing for months or years and then switched. The gut isn't prepared for new ingredients and it gets inflamed and tries to push the unfamiliar food through faster (which causes diarrhea) or tries to enclose the new food with mucus (which causes jelly-ish stool).
The solution? Don't feed your dog the same thing for months or years. Dogs are built to handle a huge variety of protein sources and different animals. If you feed variety, they can handle variety.
3) Boutique meats mean a better food.
Hmmm... the regular adult formula is $20 a bag, and the lamb and rice is $22 a bag, and the venison and millet is $25 a bag. Venison and millet sound delicious, and I love to pamper my dog. I'll get it.
This is simple math. Boutique meats are expensive. Chicken is cheap. A dog food manufacturer can put more chicken in a bag than it can put venison (or lamb, or fish, or beaver, or whatever turns it from the regular yellow bag to the cool teal-colored one). In almost all cases, the regular adult formula is the highest-quality one the manufacturer makes. The boutique meats are for dogs who are allergic to or cannot tolerate the regular proteins; they are the second (or third or fourth) choice, not the first.
4) Table scraps are bad.
Table scraps are FANTASTIC. If you read the side of a bag and it said "steak, romaine lettuce, green beans, gruyere cheese," you'd be congratulating yourself on finding the best food ever. Don't dismiss it because it sat on a plate for a couple of hours first!
In general, if you can kill it or harvest it with a sharp stick it's great for dogs. Meats (if possible, feed them raw - when you trim a steak or take the giblets out of a chicken, for example), eggs, green vegetables, most fruits, and the simple grains (oatmeal, for example) are great. If it required processing (breads, pastas, etc.) feed sparingly. If it came in a box with a label on it, don't feed it at all. Avoid feeding raw the things that don't taste good raw - potatoes, eggplant, etc. - because the reason they don't taste good is that they have alkaloids and other things in them that your mouth realizes are dangerous. In general a dog will avoid them too, but if they're mixed in with other things a dog will eat them without realizing it. So don't give him that chance. No onions, no grapes or raisins. You can feed yogurt and cheese, but avoid a lot of milk (tends to cause stomach upsets).
As long as you follow those simple rules, table scraps can improve your dog's diet immensely.
5) Diet foods are the way to keep your dogs slim. Senior foods are great for adult dogs.
Diet foods and senior foods are based on one thing and one thing alone - the fact that people like to give their dogs full bowls. It makes us feel good, and we worry that the dogs are not satisfied if they can't fill up.
In short, we're thinking like humans, not like dogs.
Pet food manufacturers know this - that we love full bowls - and so light and diet and senior foods (which are basically the same thing) have become a huge money-maker. They create a product that is dramatically lower in nutritive value, so you can fill up that bowl and the dog gets fewer calories.
Don't spend more money giving your dog substantially ickier food. Buy the absolute best food you can find, or feed a raw diet, and then adjust portion size to keep your dog slim. If that means your dog gets 1/3 cup a day, great! Dogs DO NOT NEED FULL BOWLS. They need excellent, digestible food and less of it.
6) Kibble is better for teeth than canned food.
This one has been around for a LONG time, and it's never been true. Kibble doesn't clean teeth any more than eating potato chips would brush yours. Most dogs swallow kibble whole, and the few pieces they do chew just break apart in their mouths.
Canned food is absolutely fine for dogs, when fed as an addition to dry food or even as the entire diet. It's expensive, but your dog would be fine.
What cleans teeth is having to chew THROUGH something. You can spend tons of money on the new Hills product for teeth, which is a giant-sized kibble baked so that it is like a little loofah that the dog has to chew through, or you can go spend ninety cents on a package of pork neck bones or beef knuckle bones. If you go the bone route (which is certainly what I'd recommend!) make sure you are buying RAW bone that can be completely eaten. This is not a bone the dog is supposed to gnaw on. The most easily available are pork neck bones, beef neck bones, chicken necks, turkey necks, soft beef short ribs, and END knuckle bones (the ones that are round and soft, not the tube-type beef leg bones).
If you've been feeding a variety of foods (see above) you can add an edible bone twice a week and the dog will be fine. If you've had him or her on one thing forever, expect some loose stool but it's nothing to worry about. As soon as her system is used to it the stool will firm up.
Then just start looking for those piano-key-white teeth; it's amazing how fast they clean up and look gorgeous.