You can prevent joint strain, improve posture, and build core strength by sitting activly. The key to active sitting is choosing the right chair. Most chairs provide support in unnatural ways, which cause the body to strain and slouch. When sitting on a typical chair you can practice active sitting by scooting to the edge of your seat and refraining from using the back rest.
Here’s some helpful guides for how to choose a chair and how to engage in active sitting.