I think FFF and Mr. Chung gave us 2 clues as to what will work for Fed.
1st serve must be good.
Might I add, that Fed's 2nd serve must be exceptional.
Holding serve is essential to his confidence and should keep his game loose so if the match is a close and comes down to those few crucial points he will be able to defend or play aggressively as needed. He must be confident and loose. Anything less (mentally) and Nole will take him to the cleaners in a hurry. Why? Look at him,he is the embodiement of confident and loose at the moment.
Fed must return well for one game per set (provided he holds his own serve) or during any TB's. Other than that he can coast.
As William pointed out, the important points are the BP's.
I think the strategy of trying to make a player like Nole or Nadal run, plays right into their strengths. It's a bad plan. Much better to play short points and games, thereby depriving the excellent movers and ball strikers of their timing and rhythm.
Let's hope both players bring their A game and it's competitive with no retirement from either player