After working through the first couple of chapters I can highly recommend IM Jacob Aagaard's book Excelling at Chess Calculation. One thing I've taken away so far, a point that I was aware of already but can never be emphasized enough, is to look at a wider variety of moves when considering candidates in a position. I have a tendency to narrow my focus as the game gets more complex, often considering only two or three moves, when there is a fourth, stronger possibility.
I am at a point in my chess career where better calculation would do wonders for my playing strength; I have fairly good opening knowledge and seldom come out of the opening with a poor position, I understand positional factors pretty well, and I have developed a good feel for gaining the initiative. I am rarely getting pushed around the board, even against players rated several hundred points higher. Deeper and more accurate calculation of variations is the piece that's needed for me to really make a jump in strength, and I'll be concentrating my study time on that for awhile.
We will see tonight how I'm doing when I take on a dangerous attacking player rated 2007 in many-times Reno CC champ David Ryba!