Winter...the snow, all the wonderful bare trees, people preferably dressed in dark colors, foggy days... all this makes it easier to train the eye to notice contrasts, difference in tonalities.
Since I am a big fan of monochromatic photography I used these cold winter days to convert some of my images from my recent trip to Cuba to black and white in order to make some larger prints.
The images below were converted to black and white according to Vincent Versace's technique "Black and White Photography: Learning Grayscale Conversions" in Photoshop shown at creativelive.com.