I keep a three ring binder filled with clear plastic sleeves. Any great drills I find in books I have photo copied and inserted them into the plastic sleeves, in a way making a quick reference guide to the most effective drills for me (German PAT material, Mark Wilson drills, billiard university exams, etc).
Now, instead of lugging a few books into the pool hall or looking up on a tablet (which takes time believe it or not and mentally pulls you out of rhythm)-I have my go to drills in a simple flip of a vinyl page. This maximizes time by not wasting any searching through books and also conveniently stays flat and open, not like a book which may not unless you set some weight on it to hold it open.
Inside the cover of the 3-ring binder, there are blank table diagrams so I can make notes during lessons or practice. I also have a mini daily calendar for 2016. Every time I touch a table, I log the duration and what activity I was doing: practice drills, what type of drills, or what game played.
However, I'm very strict on the hours logged. For me a true hour is when I'm shooting a 3-4 ball a minute average. If I did drills in my basement for 2 hours, I will credit 2 hours. But if I got out with friends and play 8-ball for 3 hours, I'm only giving myself an hour credit. I believe this gives me an honest assessment of how much time I'm investing into the game.
Great thread by the way and not a topic I've seen discussed here. Keeping track of your training is a great way to measure your progression.