Eyes, Nose and Mouth
Routine grooming of a horse should include attention paid to it's main sensory organs - the eyes, nose and mouth.
Horse's mouths are particularly sensitive. Taking the bit makes the mouth vulnerable to damage, and any problems should be dealt with straight away.
The eyes and nose should be kept clean and clear, and any signs of discharge investigated.
Manufacturers of horse health merchandise have several products dedicated to keeping eyes, noses and mouths "in the pink".