His face details range from a 5 value to an 8 value. Darken the lip edges to their true value with a brush or stump tip. (Remember, you will always be adjusting your values as you work so don't feel bad if you have to do it several times during the drawing.) Darken the details under his nostrils in a more detailed way using a 4h or 5h lead. If you lose the highlights along the bottom edge of his nostrils, just erase them back out. Use a brush and a little ground graphite to darken the area between his nostrils.
Blaze and Cheeks
Darken the line inside his blaze along the left side. This line has a lot of hair texture in it so you can leave your fill a little rough. This broken line continues almost to the level of his eyes. Use a hard lead like a 7h to make the little shapes that make up this line.
Darken the right cheek up to his right eye using a 4h or 5h lead.
Darken his left cheek using the darkened detail lines as your guide lines.
Using 4h or 5h lead, start to darken the detail under his eyes. Be very careful to follow your detail lines.
Eyes and Eyelids
Using a very sharp 2b, carefully outline the eyes. Use a sharp 4b to fill in the rest of the eye.
His eyelid creases are very dark. Use a 4h and a 2h to carefully darken the creases. His eyelids are a little complicated and there are creases on both top and bottom lids. Use your detail lines to help you place them correctly.
Here are some hints for handling areas with small details like eyelids:
Try using a stump to lighten a too dark area instead of an eraser.
Use your stump to make gentle transitions.
Save your highlights by hatching around them when you can.
If a detail seems to elude you in one area, come back to it later when you have a fresh eye for it.
Remember that you can always come back and add, subtract, or change detail.
Mane Forelock
Use a 2h to start filling in the dark streaks (10 values) in his forehead and neck mane. Don't be overly concerned with correct positioning, just try to get the shadows in the general areas they should be in.
A good way to get the hair shadows shaped well is to "turn off" seeing the hair and "turn on" seeing the shadows. It's a mental shift that takes some concentration but you can see that the shadows do have a rhythm and pattern if you really look at them. Just get the general pattern of the shadows blocked in and you'll have the general lay of the hair right.
Use a 4h and to darken the next darkest shadows (9 & 8 values). Use a 5h to block in next darkest shadows (6 & 7 values). If the highlights of his mane (the strands you haven't touched yet) look too light, use a stump to darken them by softly stroking them into 3 to 5 values.
Use your stump to darken the soft mane hair across the bottom of his ears, too. The hair at the bottom of his ears is soft looking, so blur the hard outline lines with the tip of your stump.
Mane on Neck
His neck is very dark and the bottom of his mane almost disappears into its shadows. To create that effect, fill in the entire area to a 6 or 7 value with a 2h lead. Then use a stick eraser that's been sharpened into a wedge shape to lift out the details of the hair.
Try to erase the hair strands in curves that follow the form of his neck. You can soften and refine these lines later.
His face details range from a 5 value to an 8 value. Darken the lip edges to their true value with a brush or stump tip. (Remember, you will always be adjusting your values as you work so don't feel bad if you have to do it several times during the drawing.) Darken the details under his nostrils in a more detailed way using a 4h or 5h lead. If you lose the highlights along the bottom edge of his nostrils, just erase them back out. Use a brush and a little ground graphite to darken the area between his nostrils.
Darken the line inside his blaze along the left side. This line has a lot of hair texture in it so you can leave your fill a little rough. This broken line continues almost to the level of his eyes. Use a hard lead like a 7h to make the little shapes that make up this line.
His neck is very dark and the bottom of his mane almost disappears into its shadows. To create that effect, fill in the entire area to a 6 or 7 value with a 2h lead. Then use a stick eraser that's been sharpened into a wedge shape to lift out the details of the hair. 
