Use the right restraint
A crash tested crate in the boot is the safest option for dogs followed by a purpose made harness clipped to the seatbelt. Cats rabbits and small animals should always travel in a secure carrier positioned in a footwell or strapped onto a seat.
Acclimatise before a long journey
If your animal rarely travels start with short trips in the week before the move. Feed treats in the carrier at home so it becomes a familiar place rather than a signal that something bad is happening.
Manage temperature and ventilation
Never leave a pet in a parked car even briefly in warm weather. Use window shades keep air circulating and carry water and a collapsible bowl.
Plan breaks and handle travel sickness
Stop every two hours for dogs to stretch and toilet. Feed a light meal three hours before departure rather than immediately before. If your animal is a consistently bad traveller ask your vet about medication well ahead of the date.
In short
Restrain properly acclimatise early keep the car cool and break the journey every couple of hours.