Hm...I wouldn't put 5/5 blitz in there - in blitz it is usually "good enough" moves that count and not the "best" possible that count. Tactics are important so that you do not give away positional advantage or miss the moment to transform it into material. Endgame is always a good place to work on since it requires proper planning - aimless moves are quickly punished, and many of the games following the book pass in an endgame anyway.
So: tactics, basic positional principles and endgame would me my pick.
Originally posted by Red NightA more complete and practical book than "My System",IMO, would be "How to Reassess Your Chess" (rev. 3rd ed.) by IM Jeremy Silman.
I like positional study and end game study at this level.
Read My System and a good end game manual. Fine's BCE in my day, probably something better out there today.
One of the best single-volume endgame books is also a Silman offering: "Silman's Complete Endgame Course."
"Basic Chess Endings" is a great reference work, even though it has many errors in it.