to log every dive, no matter how long or short, good or bad and eventful or uneventful it may be.
I fortunately dive with the same buddy probably 90% of all my dives. On occasions she is not up to another dive so I will go with someone else that I have seen dive and trust. I have logged my dive and if they did not sign off on it on that particular day then the next time I saw them they would sign off, gladly I might add. Most divers are conscientious and know that keeping the log is very helpful in maintaining records for their own personal reference as well as when the need arises to "prove" to an operation that you have developed necessary skills for a certain type of dive.
"Log Everything" about the dive including discussions prior to and after the dive, as well as the dive and equipment used, it's good practice IMHO.