Stop sitting down on the job!
There are medical studies out there that show that sitting all day is very bad for your body. The American Medical Association recommends you have alternatives to sitting when doing your daily work.
Now obviously, standing all day isn’t necessarily the answer, so the best thing you can do is to alternate. For example, I purchased this crankable standing desk for my home office:
If this is your only desk, keep a chair handy and roll it down when you want take a load off. For me, when I commute to work, I sit, but when I work from home, I stand so I get a good balance.
Standing is also no substitute for working out, of course. I recommend a you have a daily regimen of at least 1/2 hour of moderate to challenging exercise.
If you are stick at a sitting desk all day, make sure you get up and walk around at regular intervals. As a software engineer, I know what it’s like to get lost in debugging, but it’s important to “derail” and take a break. Not only that, but I find when I’m confronted with a particularly nasty bit of engineering, a good walk can clear the head and let the subconscious do its magic and present you with a solution. Sometimes, I find a good workout, like weightlifting, or some cardio, can help.