At first, you may bypass this stage of your production because you are either not interested in makeup, or think it is about wearing lipstick.
Any time you walk out of your house, you've probably spent some time getting ready. If you wake up, don't bother to do your hair, shave, have a wash and put on any clothing laying around, you're still making an impression. This is why these three items, that are often overlooked by inexperienced filmmakers and photographers, get overlooked and/or ignored.
Consider hair. If your character has immaculate hair, you are making a statement about their personality. If they wear designer gear, you're making another statement that they are wealthy, or prioritise their spend to look good. Just because your actor wears boots, does this mean your character does?
Makeup is equally important because wounds, dirt, scars all make a visual statement when we are assessing who is on the screen or appearing in a photo. If they have wounds, are they fresh or old. The placement is also important for believability. If a pupil has been beaten up, the wounds would be different depending on:
If the person is known to the character or not
Defensive or offensive
The type of weapon
The type of force (e.g. blunt force, serration, etc)
Blood isn't just bright red, the colour greatly depends on the age and type. Old blood goes dark in colour where as fresh blood is bright red.
Lighting is another factor for makeup. Different lights cause different registration depending on skin tone and the colour palette. The lighting should enhance the makeup, not cause problems.