This assumes you have a pulse motor that runs at a reasonably high RPM so that reliable measurements can be made with a digital multimeter.
For new builders or people with existing pulse motors:
1. Measure the power consumption of your motor.
2. Using a separate pickup-coil and load resistor, measure the electrical power that you can draw off of the spinning rotor and convert that into a torque measurement.
3. If you have a charging battery to collect the current pulses from the drive coil, replace the charging battery with a circuit of your own design so that you can accurately measure the power that is going to the charging battery.
4. Make a clip and present your data showing all measurements: power consumption, torque power and associated torque at a certain RPM, and charging power. Define and calculate the efficiency of your motor.