The most important thing in driving mindfully is to ignore your cellphone. When you are looking at your phone instead of the road you are in a dangerous situation.
Driving is a great time to practice mindfulness. It is a time where you are sitting down and have the most important task before you of getting safely to where you are going. When you get in the car, take a breath, make yourself aware that you are seated, and appreciate that you have the opportunity to practice mindfulness. As you drive, focus on the road. Try not to think about time, which is especially important if you are running late. Know that you will get there when you get there. If there are consequences to being late, you will face them when you arrive.
Pay attention to anger, which is common in driving situations. If another driver makes a wrong move, even a dangerous one, pay attention to your reaction. See how appropriate your level of anger is to what happened. Breathe and remind yourself to be present. Notice how others get angry in their car. If they are angry at you, realize that they are suffering from an anger problem that is bigger than whatever you did. Driving and observing road rage in yourself and others is a great time to study anger.
Driving is also a good time to practice patience. If you notice yourself getting impatient, breathe and check in with where you are and where you want to be.
Practice obeying traffic rules. Signal turns. Keep a safe distance behind the car in front of you. Be polite. Practice gratitude and wave when somebody is polite to you.
Like practicing mindfulness anywhere, when you are driving, check in with your breath, notice your posture, thoughts, and feelings, remember to be kind and compassionate. Drive in harmony with everybody on the road.