The same rules for composing an image in colour apply when you are shooting in black and white. Make sure the subject of the photo is placed in an interesting position in the shot, make sure the camera is square to the horizon and that the subject is in focus.
When you are photographing in black and white pay attention to how the colours are converted.
Some colour pairs like green and red which contrast so strongly in colour photos convert to the same shade of grey in a black and white image. Depending on what you are shooting this can be an advantage or a disadvantage.
In the image above the solid black of the nuns’ habits ensures that the image will be a strong one and placing the subjects off center makes the image more dynamic.
If you are unsure how the image will convert, check the camera’s viewfinder or on a digital SLR take a reference shot and look at the result in the LCD screen to evaluate the composition and to check that what you are seeing in the scene will render well in black and white.