To those new to drawing, seeing values can be perplexing. Most people see color instead of value. Then if something is a dark color, they assign it a dark value. That may or may not be a truthful representation. A dark color in the light can be lighter that a light color in the dark. Huh? Let me explain: If I want to draw this bowl of green and red apples, some of the shadows are on the light green side of the apples. You can also see there is a strong highlight on the deep red part of the apple in the front.
Here the green shadows are darker than the red highlight. Hence I would leave the highlight areas white or very light, and the shadow areas – no matter what color they may be – dark. Color is really not a factor when you’re drawing in black and white.
This is yet another aspect of learning to see. Practice looking for just the values as you observe your surroundings. Squinting helps to accentuate lights and darks. Another option, if you’re really struggling with this, is to take a photo with your phone and convert it to gray scale. (I checked my phone to see if it could do that – it could, then I got side-tracked for 20 minutes playing with all the edit options I didn’t know were there).
However, you don’t want to become dependent on a phone photo for your subject matter. Drawing from life is always best. Values are more accurate to your eye than through your camera lens. And, when you draw from an accurate real life subject, your drawings will be full of life too.