The easiest way to determine if you are using too much compression is to actually over compressing and listening for audible artifacts, such as pumping or breathing, and dial the settings until the artifacts are less noticeable or dissapear. Then, taking down the compression to a reasonable amount. Another way to determine if you are using too much compression is to check the amount of gain reduction being applied by the compressor. A good rule of thumb is to keep the gain reduction below -6dB. If the gain reduction is consistently above -6dB, it may be an indication that you are using too much compression.