I've completed the Concentric Square exercises. I found a rhythm as I worked my way through each piece. The first day or two, I had to calculate and really make sure I found all the squares. But after that, it was rather easy.
I generally looked at the diagonals the rook was on to find most of the squares. For the bishop, I looked at the horizontals and verticals the bishop was on. For the knight, I would look at all three. I began to see the patterns and easily recognize the squares to place the queen on for the fork or skewer. The queen was easy ... just had to look for skewers.
Now on to Knight Sight. I'll do the vision drills for a week and then I'll do the concentric square portion of it.