There are two types of health certificates available: one which approves pets for travel within the continental United States, and another which approves them for international travel.
Acquiring a health certificate will require you to schedule an appointment with your veterinarian. Your pet will receive an overall exam during which the doctor will be able to certify that your pet is healthy and safe for travel. The doctor will also verify that the rabies vaccination is current, as this is mandatory. New CDC guidelines require that if you are planning to travel to a country that is high-risk for rabies, you must obtain proof from a veterinarian of a US-administered rabies vaccination before you leave the country, so please make an appointment with your veterinarian in advance of your travel.
Please be advised that Mexico is currently considered a screwworm affected country. If you are planning travel to Mexico or any other screwworm affected country with your dog, please see the screwworm section of the USDA website.