The most important thing to do is to remove your valuables. Remember, everything you ship in your car is shipped at your own risk, NOTHING IS INSURED. Even if you are going to be shipping items inside the car we still recommend that anything valuable be taken out. NEVER ship cash, jewelry, technology, etc. Small, light, and replaceable is what to aim for, usually this means clothes. The general rule for anything shipped inside the car is to keep the total weight of everything under 100 pounds and to keep everything in the trunk or under the window level.
Cleaning your car might be necessary if the car is absolutely filthy. The car doesn’t have to be spotless but the driver will have to inspect it for damage and this might not be possible if it’s covered in dirt. Don’t think this means you can get a damaged area dirty and get money for it if the driver misses it. The driver will mark that he was unable to do a proper inspection and if he damages the car he could argue that it was there before he picked up the car, he just didn’t see it because of the dirt.
And that’s really about it. Car transport is easier than a lot of people let on. There isn’t anything special that needs to be done, be straightforward about your needs with your broker and you’ll be happy with the result.