Consider the placement of your car chase in the plot. While you want it to be exciting and keep the audience on the edge of their seats, the chase has to make sense in terms of the overall story. Think about how the chase gets started, which characters are participating in it, and the goals each of them hope to achieve. Sound story logic keeps the chase grounded within the rest of the film and prevents it from feeling tacked on.
Brainstorm some ideas for how the chase might proceed. Think about interesting stunts you may be able to perform, clever camera angles you can use, and great settings which can accentuate the action. Every chase starts with basic ideas, and while you may not be able to use all of them, they provide a good foundation to prepare a more formal plan.
Speak to your drivers and stunt coordinators about how many of your ideas are feasible, and what will be required for each one. They have a good idea of how each stunt can be executed safely and which ones you can accomplish within a given framework.
Tally how much of your budget you can afford to spend on the car chase. Your funds dictate how much you'll be able to shoot, and provide strong parameters for the scope and ambition of the chase.
Prepare a more detailed breakdown of the car chase based on your allotted funds. Use as many of your ideas as you can, while providing a structure granting the chase a viable beginning, middle and end.
Draw up a storyboard covering each shot in the car chase, the movement of the vehicles through each shot, and the general flow of the action. Not only do storyboards help you visualize the car chase, but you can also cut them together in video form, giving you some idea of how the scene will flow in the final film.
Set up each shot of the car chase, rehearsing the movements just as you would a scene full of dialogue. Give the stuntmen time to prepare, and listen to their concerns. It will make your set much safer.
Shoot your car chase as planned and send the footage to the editor for inclusion in the final film.