Two ways: The right way, and the easy way.
Here´s what I did (the right way). My roommate bought a timing light from Sears so, we popped the cam cover off and put the light on crank, and hooked it up to the No.1 sparkplug wire. Then while he timed it I turned the distributer until it was about 2 degrees ahead.
Here´s the simple way anyone can do it:
Okay open your hood up. Look just to the left of the airbox and you´ll see your dist. cap. So start your car. Hold the distributer tight and loosen the bolt. When you look at the distributer Mazda was smart enough to put a little arrow and/or mark (depending on year of the distributer). You´re going to move the Dist to the front of the car anywhere from 1/8" to 1/4. Listen for the car to sound like its revving up. You can hear the difference between advance and retard really clearly.
Tighten the bolt back up. And go grab some premium gas.
Until the premium makes it to the motor things will seem sluggish and you may even notice a knock or ping. So I recommend doing it on a near empty tank like I did. But with premium in the motor you´ll notice a little pick up from 40-65/70 on the acceleration curve.