My mother and my grandmother both put a large silk scarf over their heads before pulling any clothing on over their heads. It keeps makeup and hairdo's pristine...
You know those shower caps they give you in hotels that you never use? I take those home and put them over my face to protect my makeup from my clothes. Totally hygenic (although I have to say the pants idea is brill) and easy to throw into your makeup bag.
Put two papertowels still attached to one another so its extra long, over my face and neck then pull the garment over your head. Be sure to hold the towel close to your face and neck so it stays inside the garment. Just pull straight through and you shouldnt get a lick of makeup on there.
If you need to pull clothes over your head and you’ve already done your makeup, then put a large old pair of knickers on your head. They will protect your clothes and your makeup.
If you don't have pants/scarf/shower cap on hand, I find that in a pinch it works best if you bend forward and put your head through from the back of your neck first, then stretch the front of the shirt collar over your head (and hair), then over and way in front of your face. Harder with turtlenecks and such, but works if you absolutely have nothing else.
I thought the main worry was not ruining your makeup but getting makeup on your neckline- anyway - my mother's trick was always a pair of tights worn robber style.
Put clothes on first then do your make up and hair, wrap an old towel around you and tuck into your collar to avoid messing it up. I always put my clothes on and wrap my old dressing gown around me (since I get a new dressing gown every year) . Just be careful though, I did my make up first and realised I was running late and forgot to find out my clothes so I was running round like a chicken so I make sure at least my clothes were on as I rather go out without makeup than clothes!