When shooting black and white landscapes look for ‘active skies’. The skies with breathtaking and wonderful cloud formations will almost always translate to great black and white photography. Having skies with so much ‘action’ in them add mood and a really dynamic look and feel to images. Without this active element images will 
look rather empty and dull. I think the same principle could be applied to most types of black and white images that have large parts of them dominated by any one thing. If a large part of your image is all the same tone the image can look quite lifeless (unless of course you’re going for a more minimalist look). (photograph Golden-Gate-Before-the-Bridge by Ansel Adams)