There is no definitive answer to this question as it depends on a number of factors, including the type of car, the driving conditions and the driver's preference. However, most experts agree that a car should have between 1 and 2 degrees of toe-in. This means that the front wheels should be slightly closer together than the rear wheels.
The reason for this is that it helps to improve stability and traction when cornering or driving in slippery conditions. It also helps to reduce wear on the tyres. Too much toe-in can however cause problems such as increased tyre wear and a tendency for the car to wander from side to side.