Visualize in black and white
Think about the non-color visual design elements of your image. 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.
Train your brain for black and white by comparing the same images in both black and white and color. Most photo software lets you go back and forth between images or look at them side-by-side. A good way to teach yourself how to visualize in black and white is to look at the same image both ways. Do this with as many images as you can. I would include images that you initially intended to be black and white as well as those that were not intended that way. Sometimes you will discover great black and white images that weren’t shot with that purpose. More importantly it will ultimately help you be able to look at a color scene in the world and visualize it as a black and white image.
~Ashley Robinson from her article Digital Black and White Photography Tips and Techniques