Step 1:

Erase some of the unnecessary guidelines. Draw the outline of the eyes, which are just blocky, angled trapezoids. Make sure the bottom of the eyes line up with the slanted guideline you drew in earlier.
Step 2:

Next, sketch the outline of his hair. The hair is very large and spiky; notice how it smooths out slightly on the right side (our right, not his) of his head, though. Add more detail to his eyes and ears. When drawing his eyebrows, make sure that they rest directly above his eyes. Draw the nose and mouth next, making them very small and close together. The nose should be sort of like a blocky 'L' or wedge.
Step 3:

Next, erase all the guidelines. Add the shading under his eyes and mouth, and add detail to his ears. Next, draw the neck, muscles, and clothing. DBZ necks are usually pretty wide, so make sure the neck starts just beneath the ears. Erase any unwanted lines and clean up your sketch.