It's always worth checking the POH. From a C172 POH:
Prior to takeoff from fields above 3000 feet elevation, the mixture
should be leaned to give maximum RPM in a full throttle, static
runup.
Also know the best rate and angle of climb, from the same POH 74-72 KIAS best rate and 62-67 KIAS best angle depending on altitude.
(Figures may be dependent on model, check your own POH.)
Lots of useful information in the POH. Its use is very poorly taught.