Shooting black and white is all about capturing different tones. Not the colors, this is hard to see at first, but a trick that I've learned to help you in this process is to set your camera's creative mode up to display in black and white, but still capturing the image in color. This way you can see the effects immediately but still have all the data of a color file to get the best results from your post processing. You should always shoot in raw as well. For more detail.
Also try squinting, if you squint, you see less detail in the scene and more of the distinct tones that will become black and whites and grays.
You need to work with dynamic light, too often, dull light gives muddy-looking black and white images.
I only shoot what my Mind's Eye sees