Choose an appropriate prompt string, perhaps beginning with one of
- For a dropdown list, use Select, Choose, or Pick.
- For a text field, use Type or Enter.
End it with a noun describing what the input is, such as "Choose a state,"
"Type your message here," or "Enter the patient's name." Put this phrase
into the control where the value would normally be. (The prompt itself
shouldn't be a selectable value in a dropdown; if the user selects it,
it's not clear what the software should do with it.)
Since the point of the exercise was to tell the user what they were
required to do before proceeding, don't let the operation proceed
until they've done it! As long as the prompt is still sitting
untouched in the control, disable the button (or other device) that
lets the user finish this part of the operation. That way, you won't
have to throw an error message at the user.