You can make it a streamlined shape like a racecar.
How to make a solar panel car go faster.
This will reduce rolling resistance.
Window sill for instance by running the car in an open area away from large buildings.
Running surface run your car on a smooth hard surface.
The car can be engineered to keep its wheels on the ground.
Having a solar panel tilt on an angle can make it go slower so if it has solar panels try to put them on a level place on your car.
Match your solar power output to a suitable motor.
Course the car will run faster in a straight line than in a curve and faster on a flat course than up a gradient all other things being equal.
While solar powered cars remain the stuff of science fiction tales for most of us some forward thinking engineers have been building and racing them for years but designing a car to run on solar power is a tall order.