Stairways are always the first option when evacuating a building. Unless they are blocked by a fire, or damaged by the disaster (like in case of an earthquake) this is the way to get out of the building. Occupants who are able to get out on their own should enter the stairwell and leave the building as soon as they know there is a crisis.
Folks who are unable to leave under their own power should meet at a predestined point and wait for firefighters or other emergency personnel to help them get out of the building. It is important for those needing assistance to know exactly where the point of “pick up” will be in case of an emergency.
If you are in an office building, there should be an emergency team in charge of making sure all employees and guests know to evacuate the building. There should be steps in place to make sure all people are notified of a problem. If you have deaf employees, you should make sure that they are accounted for and being evacuated. One step to notify them of an issue is to flash the lights in the restroom in order to alert them to a drill or emergency.
No matter what – you must have a plan.
And you should practice this by having drills on a regular basis to make sure that everyone knows where to go so that you can do a head count and make sure everyone is accounted for.