Don't sit all day. Don't stand all day. Change positions (like Aaliyah said).
I love this excerpt directly from Katy Bowman's blog Nutritious Movement:
"So, we’ve got a situation where sitting constantly is creating disease and standing constantly is creating disease. Do you see the theme? Although the research and media are going to probably miss the boat on this one, the problem isn’t the sitting (or the standing, for that matter), but the constant and continuous use of a single position.
...As many anthropologists know, the way we move is mostly a result of our cultural inheritances and has very little to go with genetics. Clothing, terrain, temperature, gender, class, and fear are only a few of the many factors that affect how we adjust our joints when sitting and standing. Gordon W. Hewes reported on about 100 resting postures of the world, and I have posted this image from the study so you can see, perhaps, why our Western joint health and metabolism (which is dependent on muscle length) is the poorest in the world.
So, we need to think bigger. There is more than just sitting and standing. Create ten different options of each! If you have a standing work station, stand a few different ways every hour. When you sit, sit a few different ways every hour. Open your mind and open your joints! When you get home, stay out of your chairs and try out a lot of these Worldly Options. (Note: If you don’t have a spear, a broom may work…) Circle the ones you can’t maintain for longer than five minutes and make a note to practice that posture at the beginning and the end of an exercise session. And, parents, don’t insist that kids sit in the same fashion as us stiffer folks and allow them to explore other options. And, join them! They can teach you something about natural movement.
Also, if you do spend a yoga/stretching class cycling through10 or so of these postures, know that while this cycle is a good thing, getting back into the sitting position the other 6-10 hours of the day reduces your health just the same. Adjust the way you sit, as often as possible for a real, deep, and cellular change."