Service monitor noob inquiry.

I am new to the radio technician scene yet my responsibilities include programming radios and using the service monitor to “tune” them. specifically im using an older IFR 1500 unit. i am not familiar with service monitors at all. although i have become more familiar over the past few days. what are the key areas to be looking at when tuning at radio? or diagnosing it for that matter. i messed around with a kenwood radio today…ran the data cable to the pc and opened the software. i opened the test function and ran transmit under a few of the options. i was able to get the service monitor to pick up the Tx freq. Problem Is… i dont know what im looking for or the common options used. my question is probably vague i know but if someone could throw me in the right direction i’d appreciate it. thanks.