Hello, the checklist i follow states:
Start Up & Taxi: Tank with lowest contents.
Prior to Power Checks: Fullest tank
Fuel Pump on after power checks, during pre-take off vital actions.
Fuel pump off above 1000'
Fuel pump on for tank changes (i teach every 1/2 hour at least on a long nav ex)
Fuel Pump on below 1000'
Hope this helps