This one is so important it gets a page all its own.
Take this opportunity to check that all contract changes to on-going jobs have been reduced to writing and are signed by both parties. This discipline is not relegated only to the year-end, of course, but should be kept current throughout the project.
Commit to filing a Daily Progress Report on every job every day. It takes about a minute to file the report on your smartphone, and can be very revealing about which subs are the most reliable, what the weather was like, and when the client said what.