At a minimum, a pilot should log the flight time and the ground training needed for a certificate, rating or flight review or to document flight currency.
Pilot in command time should be logged when the pilot is the sole manipulator of the controls for an aircraft for which the pilot is rated. Solo time can only be logged when the pilot is the sole occupant of the helicopter.
There are some other conditions, but these exceptions generally do not apply to a private pilot, such as when the aircraft requires more than one crewmember.
14 CFR 61.51 Pilot logbooks