First thing to do is obtain a copy of the Pilot Information Manual from the manufacturer of the radar. For example the Allied Signal RDR-4B Pilot's Manual with radar operating guidelines ACS-5082 August 2004. Or The Rockwell Collins WXR-700X Pilot's Guide.
You will be able to find a copy in your airline technical library -or should be able to. Rockwell Collins also publish a book called "Your Guide to Weather radar". The read the books from cover to cover, particularly some of the really good advice contained on high altitude radar interpretation using a combination of max gain and tilt.
Business and Commercial Aviation magazine (USA) has superb articles on radar use. Google it and you will be amazed what comes up. Radar interpretation is a fine art, but be prepared for every pilot you fly with having different opinions on it's use.
One thing is for sure. If dodgy weather is forecast it is wise to make sure the radar is operating before you take off, and not just the test pattern. At high altitude select the Gain control (if fitted) at the maximum gain position (not auto) and this enables the radar to pick up traces of moisture in the higher levels of thunderstorms which may top 50,000.
Auto gain will not pick up ice crystals present in anvil tops and you can blunder straight into turbulent tops 28,000 and above if you happen to be in 8/8 or at night. Max gain has a better chance of picking up the tiny echoes associated with a high CB top. Once you pick that up, then lower the tilt and search for the main part of the storm.
But never underestimate the importance of the smallest echo even 3 mm long on the screen at high altitude when in Max gain. It could be the invisible to radar top of a bloody great CB. Most reports of "unexpected" or "unreported clear air" turbulence encounters that throw people around is due to lack of close monitoring by the crew of the high level tops because of poor use of auto versus max gain, and poor use of the tilt control at high altitude.
Finally, even in clear weather use the radar to watch the isolated big clouds as they pass by and compare their visual appearance with how they show up on radar. Photograph them in your mind.
Differentiate between the "soft heavy rain" that occurs at low altitudes in tropical areas (lots of red on the radar but not dangerous) and "hard rain" from CB. If the screen is covered in red at low altitude (8000 ft down) in the tropics or over water, then reducing the gain to minimum will cut out most of the red echoes. The last red echo remaining on the screen is the one to avoid. This is personal opinion only, by the way.