Respond first to signs of activity … like the T-Rex in "Jurassic Park" !
Most 'accidents' happen because someone wasn't paying attention. So, look out for movement, far and near. If you're pulling in, notice (1) what other vehicles are doing; (2) pedestrians on or near the pavement; and (3) people in parked cars.
If it's a small movement, perhaps the "other road user" is only an animal, a far-away pedestrian, or a manoeuvring bike. If it's bigger movement, it's either closer or faster … so, a bigger threat.