These are 3 simple things you can do to make it harder to steal your car, and all of them people do or have done.
1. Lock your car doors.
2. Do not leave a spare key anywhere in or on the car, as someone stealing your car would know where all to check.
3. Do not leave your title in your car. If you do, and your car is stolen, you just made it much easier for someone to sell the car. Also, if someone is just walking around and seeing if a car is unlocked, if they find your title, they may steal the car, when before they may have only been planning on taking things out of the car. I know that people have been told to leave their title in their car, so they can prove it is their car if it gets towed or something, but the registration does that, and no one can sell the car, legally, if they don’t have the title.