Standard operating procedure:
Ideally, start the motor and bring it up to operating temperature. A cold motor will show less pressure.
Remove air filter assembly
Wire the primary throttle blades wide open so the motor can breathe
Disconnect the coil hot wire to prevent a fire. Tie the wire back so it cannot arc against any metal in the engine bay.
Remove all spark plugs to make the starter's job easier to turn the crank.
Turn each cylinder through at least 5 compression cycles to max out the gauge. Each time you go through a compression cycle, the needle on the gauge will jump. ...It will stop moving after about 5 cycles.

As Ken said, most run of the mill motors will show around 130, although I have seen daily driver motors still haulin' the mail with 80 or 90 psi. On the other end of the scale, I have seen motors with well over 200 psi on pump gas with everything polished in the combustion chamber, a very tight squish/quench (think 0.030") and a "spot-on" tune. Crane cams says that somewhere around 165 is the limit for using pump gas with a run-of-the-mill street motor if you want to stay out of detonation.

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