How do you diagnose trouble code p0171 for a 2000 Nissan Sentra?

In the manual for the 2000 Sentra, page EC-306, for DTC P0171, P0174 Fuel Injection System Function, it shows as possible causes:

- Intake air leak

- Heated oxygen sensor 1 (front) (bank 1) (bank 2)

- Injectors

- Exhaust fuel pressure

- Lack of fuel

- Mass air flow.

I have read that the Mass air flow sensors are prone to fail on these cars, so you might want to have that checked first.