I agree with Rick... a great bunch of tips. Now this thread is starting to roll.
Mooh, I like your tip about using heavier strings. Sound is produced by getting the top of your instrument to vibrate and the energy transmitted to is is proportional to the mass of the string. Some people think that using heavier strings can shorten the life of a guitar but I figure if an instrument doesn't sound right, I don't want it to last too long anyway.
Good advice about the strap as well. I use a soft wide strap made entirely from leather. The wide part has as series of slots where the narrow part hooks in so the length may be adjusted. A button for the strap should be added to the heel of the neck rather close to the body but set to point toward the floor when you play. That way the heel is cradled in the strap and the strap can't slip off. If you install the button yourself, be sure to drill a properly sized hole for the screw. Forcing the screw into wood of the heel without such a hole could cause the wood to split.