Ask HN: How to take personal care when you are in front of screen for 16 hours? 11 years ago
First of all, take care of your eyes. Use the 20 20 20 rule as previously said, check your eyes to avoid headaches.
If you use a laptop, get a stand and a separate keyboard and mouse, it'll help your posture. If you have a desktop, it'll be easier to maintain a good posture and relieve neck pain by looking to what's in front of you, not down to a laptop on a table.
Walk. Get up every hour or every 45min. Do this religiously.
Drink lots of water or tea. Stay hidrated. Don't eat garbage.
To have better sleep, install flux on your computer.
If you have some spare money, buy a really comfortable office chair that's not too sofa-y and not too hard. Buy a table that has the right height to you.