1. No alcohol/caffeine - So as you might now, both alcohol and caffeine are bad for your skin. How much effect it has on your skin is individual as with all things on this list. I remember people telling me not to eat chocolate because you will get pimples, but I've always eaten lots of chocolate and I've had 3-5 pimples in my whole life. But I know that some of my friends literally get pimples over night after having much chocolate.
2. Go vegan - One of the most trending advice for skincare right now is to go vegan. I've been vegan for over a year and I can tell you that both my skin and whole body feels completely different. Going vegan is like doing a complete body cleanse. And also, foods like avocado and nuts are SUPER GOOD for your skin (and nails & hair).
3. Don't wear make-up everyday - I've never been a big make-up consumer and in high school I could go many months without using make-up at all. Nowadays I'm a bit more into cosmetics and I like trying different products and looks. But I've noticed that if I don't let my skin rest it immediately becomes tired. And when you use make-up, use a GOOD make-up remover.
4. The outdoors - I've noticed how my skin gets a totally different glow when I spend a lot of time outdoors. Go for a power walk, read a book in the park or whatever that gets you outside. I'm not quite a nature person, but I try to spend at least 2 hours a day outdoors. And whenever I don't, I can see how it effects my skin.