Switching should be done gradually, over the span of a week or two. Slowly phase out of the old and phase in the new.
The best dog food is subjective. Most high end foods tend to cost significantly more, but often contain little to no grain meal, and often use human grade foods. Sites such as
http://www.dogfoodadvisor.com/ can help you to see which foods use more higher end foods and less fillers. Some people like Blue or Wellness, (both dry) others like the tube o'meat (in the fridge at the pet food store), and still others feed them fresh food, both meats and veggies. There are a few articles on the site I mentioned that go into what most people tend to think a good dog food contains. Often your best selection and advice will come from a local pet food store. The chains are just now starting to stock the higher end foods. And at least around here, cost the same if not more than the local stores. We feed our lab Wellness, but at $50+ a 30lb bag, it's not for everyone.
Toys - for a lab, look at items in the tough chewers section. Kong is usually good...
Pretty much look at it and pull on it. If it looks like it could have come from a claw machine at the arcade, a lab will probably destroy it.
Always swap out toys. Leaving something around all the time can get them bored with it, but changing them up every few days helps to keep it fresh new and exciting.
Most of all, get training and plenty of exercise. Most dog behavior problems can be solved really fast by those two things. A well exercised dog is going to be too tired to get into any trouble. We do at least 2 30 mins walk a day. But she sleeps like a baby after 30 mins at the dog park.......