Your chin should be tucked. This stretches the suboccipital muscles. These are the muscles at the base of your skull. This is the functional centerpiece to all the muscles that run parallel to the spinal column. It is also functional centerpiece to the hamstrings, calves, and bottom of the feet. All these regions respond to the conditions at the base of the skull
Your ear hole and your shoulders should line up in the same plane. This is neutral position. For every inch your head is forward from neutral position, it is like adding 10 pounds on your head.
Please don't hold your phone with your shoulder when you talk. We can not tell you how many office workers' skulls we have to adjust on a weekly basis, and treat the related musculature
To correct slouching
The best way we know how to correct this to get a non-elastic back up chair from nadachair.com This actually keeps all your spinal curves in the correct position.
First of all, get the center of your keyboard the same height as your elbow.
The top of the screen (not the top of the monitor itself) must be at or slightly below eye level
When looking at the middle of the screen, your eyes should look only slightly downward
Tilt back the monitor 10 to 20 degrees. If you don't carry around a protractor, that is ok. Have the bottom of the monitor just above the keyboard.
A good rule of thumb: Keep the monitor at an arms distance. You should barely be able to touch the monitor with an outstretched hand. But the larger the screen, the more distance you will want.
Why this rule of thumb works:
Try it for yourself. Try the finger to nose test. The closer your finger gets to your nose, the more eye strain you get. So it makes sense to keep the monitor farther away from your eyes.
You want to position your chair slightly more than 90 degrees. Basically, you want your hips higher than your knees. We know of pilots that sit with their knees higher than their hips.
If the knees are higher than your hips, you will contract your major hip flexor muscle...called the Psoas Major. This will cause lower back pain.
This muscle attaches to ALL the low back discs and low back spinal bones. When contracted, it will compress your discs and your low back spinal bones.
Your Elbows should be at their sides, at 120 degrees or more. This will allow for better blood flow. This is because the brachial artery bifurcates (breaks into 2 arteries) in front of the elbow joint. It bifurcates into the radial and ulnar arteries.
So by putting your elbows in a more correct position, you help your blood circulation in this important area.
If you are like us, you don't walk around with a protractor (although we did in our Radiology Classes back in school). So we suggest keeping your arms at your sides with slightly more than a 90 degree bend.
An even better way to remember this angle is to just keep the center of your keyboard level with the height of the elbow.