Sure, here's that thread from a few months ago. The first person to answer is a certified fitness trainer, the second person to answer is a photographer. And there are a few other tidbits in other posts that are interesting, too.
My favorite tip for posture in general is to turn hands palms-forward as they hang loosely at your sides, roll shoulders back as you lift the ribcage, then as you allow shoulders and hands to relax, keep ribcage up. Imagery to help you pull the lower tummy in: Get ready to whistle (you don't actually have to whistle) because we all instinctively tighten tummies to whistle. Or if you imagine a zipper on jeans being zipped up.