I keep a record of mine in a database, with a printout that I take with me to the LHS.
Whenever I use a paint that has an FS number or other official designation, I put some on a ruled sheet of plastic with the designation marked below it for reference.
Paints are best stored between 65° and 75° F, out of direct sunlight. The first thing you should do when you open a bottle is clean the inside of the cap, the top of the rim, and the threads. Before you cap it up again, clean the throat or inside of the neck of the bottle, too. Tighten the cap as tight as you can with hand strength alone.