The first step is to do a deep thorough cleaning of your vehicle's interior purging it of dirt, fur, and dander.
After you are going to want to get some seat covers to protect the seats in your car. Your interior is like Velcro for dog and cat hair if you don't have a seat cover. If you have leather seats, scratches from your pet's nails are more likely. Overall, using seat covers whenever your animal companion joins you for a ride helps avoid damage and dirt on the seats.
Something else you might consider is getting heavy duty floor mats. These floor mats are typically constructed of sturdy, non-slip rubber and are designed to catch spills and mishaps of any kind while also protecting your car's carpet. These are an excellent method to keep your car clean, especially if your pet is prone to getting sick while on a road trip with you.
Overall, these are just a couple things you can do to protect your vehicle from your pets.