How to Properly Support Your Back While Sitting
Now that your chair is in the right position, you have to make sure that you are sitting properly. This is not hard, but it is harder and requires you to be somewhat mindful.
You will need to place your feet flat on the floor. Next push your behind to the back of the seat and keep your shoulders against the backrest. If you have a properly designed chair this will be enough to get you in pretty much the right position. Don't be afraid to lean back slightly- this will take pressure off of your lower back and put it on the chair.
The next step is to adjust the lumbar support. This is going to vary from chair to chair but it is critical. Without proper lumbar support people tend to lean forward and slouch over their work as opposed to keeing their shoulders backward. You don't need a lot here, just something the keep your lower back in place. If you don't have adequate lumbar support, something like a small cushion or rolled up towel can act as a lumbar cushion (though aftermarket products are sold for this). This will help maintain the right spine curvature while sitting.
That's it for now! If you are taking these measure and not achieving success you should upgrade your chair, see a doctor, or try to sit less.