Before you do that, I would draw and shade some pyramids. Draw 4 or five in different places around the page, then make a light source and shade each of them according to the light. Try to distinguish the different sides and think about how the values change when the edge is in a different location.
Kind of like this but with pyramids.

Also, if you have time check out this video on noses, she explains values and planes really well.
Your drawings look decent, but if you grasp the idea of values and how different sides are shaded based on the light source you'll be in another level. You're structure is great but the values need some pushing. Like I keep saying, you're really close.