Depends how you get paid, but the basics stay the same; altitude and duration. Some want to keep track of the load; number of jumpers, number of tandems, etc, and the way they were dispersed (two hop and pops, one tandem at 14, six fun jumpers out at 18, etc).

In the event of an incident, keeping detailed data may be a big saving grace in court. Personally I'm in favor of tracking wind conditions for each load, weather in the area, and any pertinent details (pilot chute out on the load, for example, might be an issue later, or behavior, comments, or other things observed might seem minor at the time, but be important later. A comments section, therefore, is useful.

Time off, time on, number of engine starts for turbine work, etc, are useful. I also like to track fuel uplift and use and verify that against what I indicate having burned.