In most cases you will not need to bother with balancing your motors as its usually much easier just to mount your flight controller/camera gimbal with some foam/anti-vibration material. Also it seems that having a balancer propeller plays a much bigger role on vibrations. However if you are after a very vibration free system (or your motor has some vibration issues), then this video below will show you how to go about balancing your brushless motor using a smartphone by using a accelerometer monitor app.
If anyone else knows of some useful videos or tutorials on balancing your motors then post them below!