How much Should a Diode Read on a Multi Meter?
The answer depends on the type &amp; condition of the diode you measure.
Typically, a good, forward-biased silicon diode will have a voltage drop measurement of 0.5V to 0.8V.
A good, forward-biased germanium diode will have a voltage drop measurement of 0.2V to 0.3V.

It's usually best to test the diode out of circuit. 
You should also test the diode in both directions to ensure that it blocks current in one direction (i.e. shows no voltage drop (i.e. 0V) when the diode is reversed-biased).