Lou has kindly compiled this check list of things to check before sealing the portrait. I don't actually have any fixative spray (I didn't know you needed that for pencil) but it might still be a useful list.
Checklist
1. The Eyes
• Is the shape correct?
• Are both pupils looking in the same direction?
• Have you included every small crease line?
• Have you added the highlights?
2. The Nose
• Is the shape correct?
• Are the nostrils the correct size?
• Have you used spherical shaping techniques?
• Have you added the highlights and shadows?
3. The Mouth
• Is it the correct shape?
• Have you missed any lines?
• Have you remembered the dimples?
• Have you added highlights?
• Have you made the corners darker?
• Have you remembered the clevis above the mouth?
4. Shape Of Head
• Have you got the shape correct?
• Are you sure you haven’t come to wide with the outline?
• Have you got the size correct?
5. Shading
• Are all the tones correct? Look carefully!