What are the 3 quantities that may be considered as parameters in order to change the speed of a dc motor?

From my understanding of electronics: The input voltage -- generally the higher the voltage, the faster the motor will go. Of course, this will shorten the life of your motor. The motor itself -- Different motors are designed for different applications (i.e. high torque, high speed, etc.) Gearbox (a.k.a. transmission) -- Can increase the speed of a motor with a sacrifice of torque or vice versa.