Answer
Use 180 or 220 grit dry, sand with the grain, and blend the area so you do not create a low spot.
Why it happens
Pencil graphite can sit in the grain and needs light sanding without creating a low spot.
Recommended grit
Use 180 or 220 for pencil marks. Use 120 only if the mark is deep or the area is rough.
Wet or dry
Dry.
Success check
The pencil mark is gone and the area blends evenly with the surrounding wood.
What to do
- Try light dry sanding with 180 or 220.
- Sand with the grain.
- Blend the area into the surrounding surface.
- Remove dust before finishing.
Avoid: Do not dig a low spot into the wood just to remove a mark.