Keeping the air vents and cooling fins clean off debris, so the motor can dissipate it's heat.
Check that the machine it is driving, has no binding rotating matters which could slow the motor down, or make starting more difficult.
Do a load check when the machine is running and check that the current measured, is within the nameplate rating.
Check mains voltage too. Undervoltage to motors will reduce starting torque and may cause a motor to stall and burn out prematurely.
Check thermal overload settings set correctly.
Check fusing. Correct size, motorrated.
When fully isolated from the supply.
Check end play on bearings.
Do an insulation test on the windings.
Hope this will help
Kind regards, Raymond
The product of rotation, excitation and flux produces electricty.