Dogs are commonly poisoned by eating toxic plants, so check all your household plants and landscaping to make sure your dog cannot access any dangerous ones. If you have pest control or use herbicides on your landscaping, make sure that they are safe for pets or that your dog cannot get to them.
If you do apply dangerous chemicals to your yard, make sure you keep your dog inside until it is completely dry and safe. Keep your dog in another room while you use household cleaners as well, since drinking those can be hazardous and the fumes can be irritating to the dog. When not in use, make sure to store the cleaners out of the dog's reach in a cabinet or another closed storage area.
Both prescription and over-the-counter medications can be hazardous even in small doses. Store them high up and behind a closed door, such as in a medicine cabinet. If you drop any while taking them, keep your dog out of the room until you find the dropped pill.
Many foods that are safe for humans are dangerous for dogs, so store those in a refrigerator or cabinet. Consider crating your dog when you are not home or using childproof latches if your dog can open cabinets.
Keep the phone numbers of your veterinarian and an animal poison control hotline available in case of emergency.