The address, and the entrance that matters.
Give the street address and any unit or suite. Say whether the issue concerns a front door, side door, private apartment entrance or shared entrance. If a gate or another access point affects reaching the property, explain that too. Discuss availability for the actual address rather than relying on a town name alone.
For a parked vehicle, provide its current location: the parking entrance, row or level and a nearby clear marker. A shop or event you visited may be a different place from where you left the car.
A few details help identify the request.
For locks, explain whether a key is inside, missing or difficult to turn, and whether the door can be secured. For vehicle keys, have the year, make and model ready and say whether a working key remains. For an overhead garage door, describe its position and visible behavior without trying to diagnose a component.
If you are a tenant, manager or arranging help for someone else, identify the person who can approve the proposed work. Ask what authorization is needed rather than assuming a particular document will be accepted.
Before agreeing to the work.
Ask about availability, the intended scope and what the estimate includes. Confirm any applicable visit, labor, parts or programming charges and what still depends on inspection. You can make an initial enquiry without knowing the name of the service you need.