Don’t do anything new. If your dog is not used to car travel, acclimate him first. Start with short trips around the block and slowly graduate to hour-long neighborhood and highway cruises. Also, go to fun places like the dog park or to visit friends. You want your dog to think that trips in the car are fun and that not all of them end up at the vet's office!
Use a safety harness or crate. Decide where your pooch will ride and consider a pet vehicle safety harness or a soft dog crate. Crate training your dog weeks before your trip will make everything easier because if you are forced to leave your dog unattended in a hotel room, leaving him in a crate is the best option (if the establishment allows you to leave your pet alone in the room; some do not). Having a portable dog crate at your destination is convenient as well. It not only provides a place where your dog can feel safe, but it will provide you with peace of mind knowing where he is at all times when you are not around. More tips here.