- Consider designing your space so you can stand at your desk periodically. It's a nice change of pace for your back. I have a pretty cheap Ikea desk with a motor that raises and lowers it, but you can also get a Varidesk or use milk crates or something similar.
- Get up and walk every hour or so. Do a quick chore or check the mail or something.
- Keep hydrated. If you use normal-sized drinking glasses, this can dovetail nicely with #2.
- If you start to get pain in your arms or fingers, invest in a wireless curved keyboard. I use a Microsoft Sculpt and love it.
- Setup your chair, desk, monitor, etc. so they are ergonomically sound. Mayo Clinic has some advice on office ergonomics.
- Not everyone can locate their home office in a separate room like I can. Still, you need a space, and you should find a way to physically check in and out of "the office." When I started working from home, my space was in the family room attached to our kitchen. Not ideal, but it's all I could do at the time. To check in and out of the office, I would turn the monitor off. Though I could still check and reply to emails on my phone, having the computer/monitor off helped me set a boundary.
Pay attention to your physical work space. If you don't take care of your body, it will punish you.