"Many pilots get hung up on the order of the data that you should report. The Flight Watch specialist will prompt you for the information if you've left something critical out. My suggestion is to first write down the report before you call them so you don't leave something out. After the initial contact, make sure that you at least report your location, altitude and aircraft type along with whatever other information you think is appropriate. Reports of cloud tops, turbulence and icing are the most critical. And remember, don't feel bad if you are only reporting those severe clear conditions. They're very important, too.
Pilot reports are very subjective and often depend on the aircraft type and the pilot's perception of the event. Here are some general guidelines for reporting turbulence. Imagine holding a cup of coffee that is nearly full. In light turbulence you can usually avoid spilling the coffee. In moderate turbulence, the coffee will slosh around a lot and will spill out quite frequently. In severe turbulence, the entire cup of coffee ends up on you with a very brief loss of control of the aircraft. And extreme turbulence…well, you've got more to worry about than some stupid cup of coffee. As you can see this image from an FAA advisory circular is somewhat outdated, but it might be a good memory aide.