The parking brake
You should normally apply the parking brake whenever the vehicle is stationary. Apply the parking brake and put the gear lever into neutral when you're stopped at traffic lights or queuing behind other vehicles, unless the wait is likely to be very short.
Your foot could easily slip off the footbrake if, for example, your shoes are wet, or if you're bumped from behind. You could then be pushed into another vehicle or a pedestrian.
Always leave a safe gap between your vehicle and the vehicle in front while queuing, especially on a hill. This will give you room to manoeuvre should the vehicle in front roll back or should a driver behind come up too quickly.
Always keep an eye on the mirrors.
The use of the parking brake is even more important in vehicles fitted with automatic transmission. The parking brake will help avoid the possibility of 'creep' the vehicle surging forward if the accelerator is pressed accidentally while in D (Drive).