If a cop is pulling you over, go to a safe, well-lit area with enough room for both cars. On a highway, pull over to the right side of the road. If you can't slow down and pull over immediately, turn on your emergency lights to let the officer know you will pull over as soon as possible. Once you pull over, roll down the window, turn off the car, and keep your hands on the steering wheel. If the cop is in an unmarked vehicle, you may wish to keep the window rolled up until you see their identification.
Be calm, polite and respectful, not defensive. When the officer asks to see your license and registration, let them know where they are before reaching for them.
You may or may not get a ticket. When the officer is done issuing the ticket or warning, use caution when making your way back onto the road.