Store your feed in a dry area. Be sure feed is not contaminated by mold or mildew. Treats are fine in moderation and most welcomed by most critters. Never feed them chocolate as well. Lettuce is dangerous for many species as well.
Some wild berries are toxic to certain species as well.
Check with your veterinarian. Which brings me to one of the most important issues on keeping your animal healthy. A VET Ideally, find a veterinarian specializing in exotic animals. If you are searching for an exotic animal veterinarian, ask a exotic animal breeder or your pet store if they can recommend one in your area. If there is not one available, find a veterinarian that has an interest in other species and is willing to learn about your animal.