First and foremost, make sure it works. Make sure all of the shutter speeds work, particularly the slow speeds. Check that the viewfinder isn't too dirty.
When the shutter is released, the shutter closes, the mirror flips up, the aperture closes to the desired opening and the shutter then fires. All of this should happen almost simultaneously.
If the shutter needs to be serviced, the shutter will close, the mirror will flip up, the aperture will close and then nothing. Or the shutter will fire after a short delay.
See if the selenium meter still works. If it's snappy, then it probably works. If it is sluggish, use a handheld meter.
The camera does not have a rapid-return mirror. When the shutter is released, the mirror flips up and stays up until you wind on to the next frame.