Add key details and sketches while you are actually observing subtle details are almost impossible to remember later on. Check your watch frequently and get in the habit of jotting the time in your notes. Fill in less important details and finish sketches as soon as possible after the session. With a little practice note taking will become relatively painless. An index will aid you in finding particular entries.
Chronological notebooks are the most traditional form of astronomy log.
Sectional logs have sections or compartments for organizing an astronomer s notes. The first section might be just for lunar observations, the second might contain notes on deep-sky objects, the third just sightings of the planet Jupiter, etc. Although sectional logs are more organized than chronological logs they may take up more shelf space. Keeping your log in separate notebooks or ringed binders will cost more than using a single logbook, but this option is the most flexible if your interests are varied or subject to change often.