Getting “doored” occurs when a driver or passenger opens a car door without checking for oncoming traffic, resulting in the cyclist crashing into the car door. These crashes happen to urban cyclists all of the time, and can cause horrific injuries. Unfortunately, many normally careful drivers just don’t think to look before throwing open a driver’s side door, even when they’ve parked on a street with a designated bike lane.
Ideally, the way to avoid being doored is to ride with enough distance between you and the parked cars to your right so that you are able to pass an unexpected open door. However, in traffic or on narrow streets, this practice isn’t always possible. When I’m riding in an urban area, I always keep a sharp eye out for occupied driver’s side seats. If there is someone sitting in that seat, I assume (for my own safety), that they will not look before swinging the door open, and I take preemptive action to avoid the potentially dangerous situation.
Always be sure that you have the clearance to move to the left when avoiding open doors or potential open doors - you don’t want to end up getting clipped by a moving vehicle from behind in an attempt to avoid a car door.
Be hyperaware of your surroundings. Ride in control and at a reasonable speed in congested areas so that if you do encounter any combination of these scenarios, you have the time and ability to react. Ride defensively, and make sure that you’re paying close attention to your surroundings in case someone else is not.