Without color the components of visual design become that much more important. Look at the lines in the image. Are they horizontal? Vertical? Diagonal? Do they form a pattern? Rhythm or repeating elements in a photo are interesting, with a break in the repetition being even more interesting. Also look at the texture, shapes, and forms in the image. Concentrating on these will take your mind off the color and enhance your ability to “see” and think in monochrome.
~Joel Wolfson from his article Digital Black and White Photography Tips and Techniques