It really helps to do a lot of value sketches to see and really “sink in” to your subject. In painting, there’s a lot of thinking going on with color, brushwork, and other technique issues. So many times in my paintings, it was an issue of forgetting to focus and observe my subject. My brush is moving, but I’m not taking the time to look and record. Sketching will re-focus you into accuracy, squinting to get the values right and also, you can let go and let your mind work out the patterns needed which would be a disaster in painting. In painting that’s a straight road to overworking the subject until it’s color is mute and looks dead.
A new “toy” I’m using for this is a wax “Sanford Peel-Off” pencil used for marking metal (welding pencil). The other two pencils are a white General charcoal pencil and regular 0.5 Bic mechanical pencil to lay in the undersketch. The wax pencil has a benefit over charcoal in that it’s keeps the tip sharp easier and you can use the eraser to blend it out. The more you erase, the thinner the coat is until it’s like a transparent layer. Perfect for edgework to soften edges far from the focal point.
If your up to practicing this, start by marking four values on the bottom corner, dark black, light black (wax pencil with lighter touch), leave the tan to be the next lighter value, and finish with the white charcoal. Draw in your subject lightly with the mechanical pencil, then shade in the white and darkest darks. This should help you define the focal area well since it normally has the highest contrast. Next shade in the rest and don’t forget to leave the tan paper blank where it’s already the correct value. When you finished shading, if you want to soften up the edges away from the focal area, use the eraser to move the wax around. You might need to scrape off the eraser if it builds up. Keep erasing until it looks right. You can go back over it with the wax pencil if needed, but the white charcoal will not work over the wax. So, make sure you keep away from the white. Have fun!