
There are two main ways of installing aftermarket GPS unit brackets in a vehicle - a suction cup with a stalk attached to the windscreen or a Velcro pad on top of the dash.
Whichever is used, the objective should be to have the GPS screen as close as possible to your eye-line when looking at the road ahead without blocking your view of the road. This indicates a position on either side of the steering wheel, depending on the shape of the dash in your car.
You may find it easier to change focus between the road ahead and the GPS if you place the unit further away rather than close. Most units have voice prompts for navigation so it is not essential that you are able to read the screen while driving - in fact, from a distraction point of view, it is desirable that you don't look at the screen while driving.