Final answer:
When cleared direct on an IFR flight, tracking is the procedure that should be used to maintain a straight and accurate course towards the destination.
Step-by-step explanation:
When cleared direct on an IFR flight, the procedure that should be used is tracking. Tracking involves following a predetermined course or route using navigational aids or instruments. Homing, on the other hand, involves using a navigational aid or instrument to return to a specific point, which is not necessary when cleared direct. Tracking allows the pilot to maintain a straight and accurate course towards the cleared direct destination.