How do you actually sit properly?

Tuck your lower back in. Don't rest your weight on your arms. Try not to let your back muscles fall into disuse by leaning on the chair back. Whatever chair setup helps you achieve these is probably fine.

For me what works well is backless chairs that allow me to angle my thighs downward slightly and tuck my feet underneath me and to the side. Right now I'm on a yoga-ball-chair (basically a yoga ball that does not roll). Previously I sat on a large round ottoman.

on a similar topic, I recently watched this great video by WSJ where an ergonomics expert explains how to sit and how to setup the desk - https://www.youtube.com/watch?v=F8_ME4VwTiw

Raise your monitor to eye height instead of curving your back to peer at a laptop screen that’s near your hands. Once you do that your spine will fall into its natural position.

I work out rigorously and regularly, focusing on core and upper body strength. I take brisk 6+ mile walks several times a week. I have a super ergonomic chair with little levers and gauges to configure it in minute detail. I still get massive neck and shoulder pain if I don't sit in a way that gives me the posture of a cheeto.

I have long since opted for painless over imposing, but if you're one of those lucky persons who can stand up and work, that's probably your best bet.

I stand half the time (my desk is adjustable). When sitting I lean far back and slide in to avoid putting too much pressure on my lower back. Sitting up straight for long periods is unhealthy. The ideal angle is between 120 and 135 degrees. http://news.bbc.co.uk/2/hi/6187080.stm

I just picked up a kneeling chair and it's been an adjustment. It's nice though -- it sort of forces you to keep your spine and neck in a good position. This is the one I got: https://www.amazon.com/gp/product/B07W99RSZK/

It is important to have your core engaged. This doesn't mean applying a maximal level of force, but you should maintain control of your spine.

It is OK to lean towards your computer, lean back, do all sorts of weird things -- if you do the work to maintain your spine and neck position. In fact, you should vary your position as you work, take breaks, etc.

Your body weight should be supported by your hamstrings, not your lower back. You should feel a little strain in your thighs.

Here's one article providing ideas but note the page date! https://backintelligence.com/proper-sitting-posture-at-a-des...

BTW it's important to regularly get out of your chair too.

I agree with what everyone is saying.. it makes complete sense and I'm fully aware I should be doing these things.

The problem is I don't remember to, or it slips my mind throughout the day. Any quick hacks you know of to help? I heard of one where you just keep a post-it on your computer to remind you..