A couple for getting started, but nothing for mid-dance correction or reminding:
Very similar to Amps's...stand with feet together, and image that you're reaching up to get something off a high shelf. Not so high that you have to stand on tip-toes, though. Feel how your weight comes forward a bit over the arch-to-ball area of your feet. Feel how your ribcage is lifted, and your abs are slightly pulled in. Lower your arms, but feel that position remaining.
For weight over feet...stand with feet together, or slightly apart, and slowly rock from back to front and back. Feel the weight at the back edge of the heel--but not so far that you feel like falling or taking a step; feel it straight down; feel it through the arch; feel it in the ball of the feet; feel it go further forward than that--but not so far that you feel like falling or taking a step. Learn to feel those differences and control the shift.
For posture...stand with feet shoulder-width apart. Bend your knees and ankles and lower as far as you can go. Then, thinking about pushing evenly with your entire foot, think about pushing your body up and your feet down into the floor. Slowly push yourself so you're standing straight...and keep pushing. Keep your feet flat, keep your shoulders relaxed, but feel the push up through the top of your head. Think about making yourself as tall as possible. Feel the separation of your ribcage from your hips, and the looseness that comes from it.
Also, imagine a string connected to the top/back of your head, pulling you up.
For angle of hips...stand with feet shoulder width apart. Take one hand and place it so that your palm is facing your body, with your thumb at your navel and your pinky at your belt buckle or thereabouts. Rock your hips to the back, so that you go sway-backed and the hand on your belly stretches open wide. Image pushing your belt bucle away from your belly button with your fingers. Then, imagine pulling your belt buckle (and hips) up towards your navel, bringing your pelvis forward--through a "neutral" position, and tucked under. Feel the difference between tucked under, neutral, and sway-backed. You're aiming for neutral when you dance.