Below is a Value Chart
Practice these values going from light to dark, and dark to light daily till you get comfortable doing them. It may seem repetitious, but it will pay-off in over time.
Observe the incorrect blending technique in the following image. This way of blending will not give you a smooth and even finish.
Observe blending technique in the following image. This is the way you want to practice blending. Regular practice by gradually apply less and less pressure on your pencil with each stroke.
Note: All images the above images enlarge by clicking on them.