First clean the interior.
Toss all trash. Remove any items that don’t belong in the car.
Tackle the floor mats and the tricky spots.
Slap the mats together to remove dirt, then lay them on the driveway. Vacuum using a wet-dry vac that has a blower feature (like Shop-Vac 10-gallon wet-dry vacuum). With the hose connected to the exhaust port, blow debris out of the space between the seat and the center console. Return the hose to its original spot (for the next step).
Dust cracks and crevices.
Rub a clean toothbrush along the dashboard and the door panels to unearth debris. Follow with the vacuum hose to suck it up.
Vacuum the floor and the upholstery.
Move the front seats all the way forward to reach the area under them from the backseat. Move the seats back and vacuum the floor in front. Finally, recline the seats to get as far into the crevices as possible to retrieve any lingering dirt.
Wipe down the dashboard using a damp microfiber cloth.
Move on to the middle console, gearshift, steering wheel, door handles, cupholders, and seats. Apply an auto-specific cleaner (like ACDelco’s) with a new cloth, skipping the seats unless they are leather.
Clean the seat belts.
Dip a cotton cloth into a cup of warm water with a few drops of laundry detergent; wipe.
Degrime the windows (and the sunroof, if you have one), starting with the interior.
Apply a foam cleanser (like Invisible Glass), which doesn't drip like a liquid formula, and wipe with a microfiber cloth. Work in an S-motion horizontally, then use a vertical S-motion on the exterior. This way, you will be able to see which side has streaks (if any) and needs another pass. Roll down the windows a bit and swipe the top edges, too.
Replace the floor mats.
Then make sure that all the doors and windows are closed!
Then tackle the exterior.
Hose down the entire car, paying special attention to the tires (and the panels behind them), where debris and brake dust collect.
Start the scrubdown.
Fill two large two-gallon buckets with water. To one, add a few squirts of an auto-specific soap (like Meguiar’s). With a car-wash mitt or a sponge, apply soapy water liberally over the exterior, rinsing the mitt periodically in the bucket of plain water to avoid scratching the finish with clinging debris. Wash in this order, hosing off after each: roof, hood, and rear, upper portion of each side, lower portion of each side.
Clean the tires (rubber portion) and wheels (metal or coated alloy rims) using a second mitt or sponge.
You may need a wheel brush to reach smaller spots.
Thoroughly rinse the car using the hose.
Dry immediately with a chamois or cotton cloth, working in a circular motion from high to low. This way, as the drips move down, they won't rewet the area you just dried.
Wax on, wax off.
When the car is fully dry, add a shiny, protective layer: Use a cloth to apply wax (like Turtle Wax Ice Liquid Wax) according to the directions. One coat lasts about three months.
If the headlights have dulled or yellowed, revive them using a kit that sands and polishes the lens* (like 3M Quick Headlight Renewal).
Now hit the brakes (ha).
*Restoration kits can cause damage to a car’s paint, so use with care or consult a professional.