It is not enough to be a good player; you must also play well.

A very important point to note. The only way to make that transition is to play frequently and analyze your mistakes afterward.

Anyway, despite the fact that I certainly have more than enough chess books (my endgame library of a handful of books is more than sufficient to take somebody from rank beginner to master in that discipline if combined with plenty of practice), I decided to purchase Lasker's Manual of Chess. In my defense, I need to start from the level of a "stupid person" and my library does not have any books that quite fit in that range. The lowest level of book I have is probably The Amateur's Mind. I certainly have enough "strategy" books and "tactics" books. I might be able to justify purchasing Yusupov's books later, too, on the same premise. One can always justify purchasing collections of annotated games.

What convinced me to pull the trigger on it, though, was that a friend of mine who is also getting back into chess recommended it. That was enough to push me over the edge.

EDIT: The above about endgames is not quite true. I think Shereshevsky's Endgame Strategy might be necessary as well to get up to master strength in the endgame, or at least very helpful. In case you're wondering what endgame books I have, I have Averbakh Essential Endings, Pandolfini's course, Silman's course, Minev's Practical Rook Endings, Mueller's Fundamental Chess Endings, Secrets of Pawn Endings, Secrets of Minor Piece Endings (in my defense, I got it years ago on clearance), and Dvoretsky's course. I've worked through Pandolfini and part of Silman, have used the pawn endings book as a source of exercises, and have read parts of Averbakh and Minev. When I get to the stage where I'm studying endgame stuff again, I think I'll go through in roughly that order and make sure to play through a lot of examples with a clock against the computer.