I agree with Dechi and fjm. A clean shaved face looks much better and is easier to maintain, especially on dogs that are lighter in color (meaning essentially any color other than black but even black dog faces can look bad with stuck food and stains if left on the fluffy sides).
I love shaved poodle faces, but I do keep a light colored poodle mix with a donut mustache. Since you asked I will dispense some advice.
1.Everyone is right, shaving it is the way to get rid of it.
2.Do a deep review of Japanese face grooming. Notice how they tend to keep the hair on the lower jaw very short,leaving the hair on the upper snout longer but still well trimmed. This technique prevents a lot of staining.
3. Wipe and dry face everyday, and more frequently if they are eating raw or moist foods.
4.For dental health it is very important for the hair to not be allowed to be in the mouth.
5. using an appropriately sized greyhound comb, comb the face every day. If you discover crusties, add in an extra face wash and dry.