• I get up from my chair regularly (I've been having back problems for years, so this is crucial for me). At the office I'd just go to the water fountain regularly - maybe every 20 minutes or so. Now that I'm working from home, I listen to vinyl records while working. This forces me to get up regularly to change sides or get another record.

• I have an ergonomic chair (AllSteel Sum), I use a vertical mouse (Evoluent Vertical mouse), an ergonomic keyboard (Kinesis Freestyle) and a keyboard tray set to the correct height (it's not always what looks comfortable - look online for proper settings). Monitors are also set to the correct height (actually I'm lucky, they just happen to be the correct height on my desk...)

• I try to steer clear of junk food as much as possible (that wasn't always true, but nothing like a health scare to set you on the right path). Lately my morning snack is a couple of clementines. But keep in mind that a less-healthy treat from time to time can also do the brain and moral some good - all in moderation. :) I used to weigh nearly 220 pounds a little over three years ago and I'm now at 163. Keeping junkfood in check and being mindful of portion sizes has a lot to do with that.

• I try to go for a short walk in the morning and after lunch. It's good to get some air and move around. And sometimes I find the solution to a problem while thinking about it while walking - the brain approaches it differently when you're not staring at it on the screen.

• Don't spend all your time on the computer. Read, get a hobby, exercise (I alternate between gym-ish exercises and yoga). Basically, get your mind off programming.

These are some of the things that have helped me:

• Exercise; If I don't exercise regularly, I feel like crap, and I'm less productive and more stressed.

• Try and socialize regularly.

• Do other stuff apart from programming, like painting, create music, listen to it... this can stimulate the brain in different ways and help you be a better programmer.

• Eat well and healthy, don't take to many stimulants.

20 years dev here. A few thing I must do in oder to stay healthy. I need to walk 20-30 minutes per day minimum, if I don’t do that I get terrible back ache. In a good week I workout 2-3 times with fairly heavy weights and I do yoga 1-2 times, I should do cardio a few times a week but I never do. Side projects are also something I do to keep the learning flowing. Being comfortable at your desk is important but it means different things for different people. ANC headphones allows me to focus and block out the noise of the office. 2-3 liters of water per day plus several tea and coffees, that also helps by making you take more toilet breaks. I often take an extra walk once in the middle of the day just 10 mins near my office. My favorite apps, calm radio, daily yoga, Fitbod.

Stay off the carbs, keep your sugar low. No need to spike your insulin while sitting all day.

Some of these are things people have already suggested, but here goes:

• Water - keep yourself hydrated. I've been dieting for the last week, and as part of that I've been drinking far more water than normal. I feel better for it.
• Nutrition - have a variety of meals rather than the same things all the time. This can get difficult, but changing a couple of ingredients can mean the same "boring" food gets a new lease of life.
• working environment - make sure you have your workspace set up right. Monitors are eye level so you aren't looking up or down. Have a wrist rest for your keyboard if you need one. Get an ergonomic mouse if required. And make sure you invest in a decent chair. You're going to be in it for a lot of time.
• Exercise (I don't do this remotely close to enough) - something as straightforward (for most) as walking can be hugely beneficial. You don't need to go and run 10k each day, just get out for some air. On top of that, making time to stretch each day so you don't get muscle tightness from sitting inactive
• take a look around - staring at a screen all day isn't great for the eyes. Nor is averting your gaze to look at the wall which is 6-inches behind it. I've recently rearranged my home office so I can look up and look out of the window. The difference in being able to look so far is resting my eyes so much more. And I get natural light when I want it.
• Avoid energy drinks - this is coming from someone who used to have one a day, as well as coffee. They are loaded with all kinds of additives, even the sugar free ones. They are awful for your teeth and gums. Save them for the 24-hour hackathons when you really need the stimulation.
• sleep - make time for it, and get what you need. Some people need more than others. Some are 3-hours a night, some are 9 or 10 hours a night. I know that I need at least 6.5 hours to have a good day. Much more than 8 is usually too much for me.
• take a break - this is both during the work day, and after. Don't sit glued to your computer or other devices. Make time for the exercise, or a hobby which doesn't involve a screen or...
• social interaction. It's a great stereotype that developers are loners who would, if they could, avoid all contact with anything resembling humanity. The reality is we are human. We are social creatures who need some level of interaction. Just talking to somebody to build some connection is, chemically speaking, good for us.

There's so many other things which could go on this list, but remember not just to focus on your physical wellbeing. Mental health is just as important. Possibly even more so, as if you're in a bad place mentally you may not feel the need to look after yourself physically. Mental health is overlooked far too often, which can lead to awful consequences for all involved.

In addition to all suggestions here, more important is to maintain a proper sleep pattern. Avoiding coffee very late in the evening helps in this as well.

Eat well (according to your goal)

Exercise

Drink water

breathe

Exercising regularly, doing this outside of programming( if you don't like anything else then just go for a walk). Know it is okay to take a long break.

I think taking breaks to do some stretching is fine