Use the ABCDE Method Continually
Tracy's ABCDE method ranks every task by consequence. 'A' means something you must do with serious consequences; 'B' something you should do with mild consequences; 'C' something nice to do with none; 'D' something to delegate; 'E' something to eliminate.
Where you have several A tasks, number them A-1, A-2, A-3. Your A-1 is your biggest frog. The rule that gives the method its power is simple: never do a B task while an A task is left undone.
Run through this labelling on your list before you start working. A minute of prioritising prevents an hour of busy, low-value effort.