Warm the motor up to proper operating temp. then kill it, put compression adaptor into sparkplug hole, hold throttle open, and kick the beast untill the little needle won't go anymore. Repeat a few times to correct.
Kick the bike thru more slowly than you would to start it. The decompressor won't open. It's a fine line between fast enough to "pump" the air, and too fast - sometimes it works and sometimes it doesn't!
Make sure you have the throttle wide open, otherwise the engine doesn't have a good air source and you'll get a low reading.