As I understand it, prior to the point of dispatch the crew should refer to the MEL for guidance with regard to their fault. After that the QRH or any other inflight procedures should be applied (such as ECAM drills on an Airbus).
However, after the point of dispatch consideration should be given to the MEL and its implications as they could prevent further dispatch (e.g. if the flight is outbound from an engineering base to an out-station with no cover).
A report I read where a BA 744 departed, and during the taxi had an EPR guage fault and reverted, quite correctly to an N1 mode. Fine, the a/c had taxied away under its own power so the crew simply refered to the QRH for the procedure.
Had the crew also refered to the MEL they might have spotted that this fault would inflict a performance penalty. Given the weight of the Jumbo at the time, they would not have been able to take-off.
Fortunately the B747 departed without incident.
Jackoff.