I just went through a fabulous posture workshop with Esther Gokhale that helped me understand proper pelvis alignment. Here is a quote from a message forum where Esther answers a question similar to yours:
http://egwellness.com/forums/8-steps-–-questions-and-discussions-related-book-“8-steps-pain-free-back”/8-steps-general--17
Anterior tilted pelvis: this is not a problem. If your pelvis is truly too tipped, you'll back it up some and if it just right, you'll just skip some steps and go on to follow the other directions. In my experience, however, often people who think they are too tipped are actually swayed + tucked. It is easy to mistake a sway for an anterior pelvic tilt - both send your bottom back - it's the location of the curve that is critical. Tipped pelvis gives you a curve very low down in your spine (at L5-S1); a sway gives you a curve higher up in the lumbar spine. If it is a sway you have, you may still need to work on tipping your pelvis forward, but not till after you straighten out your sway.
I recommend Esther's book, 8 Steps To a Pain Free Back. I found it to be a good first step to fixing posture but there's nothing that can substitute for the hand's on training in her Gokhale Method Foundations workshop.
http://egwellness.com/classes-services/gmf It was well worth the cost. The difference in my shape, strength and running ability are all proving that to me. When I get some spare time I hope to post a more detailed review and some before/after pictures.
Esther teaches that proper posture is NOT with a tucked pelvis (as is often taught and what I previous believed). The trick is to anchor the rib cage down using the core abdominal muscles (especially the obliques) so that the lumbar spine is not swayed. Release the lower back and hip muscles that would tuck the hips so that the pelvis tips naturally at the top of the butt. She refers to it as getting your behind behind you. Imagine that you have a tail (like a dog's tail) and be sure to sit and stand with your tail out behind you; don't sit on your tail and don't stand with your tail between your legs.
For the upper body, imagine that you are trying to lift your chest up and over a bar at chest height. Elongate the spine and use your abdominal muscles to pull the bottom of the rib cage down and back. Now roll each shoulder (one a time) a little up, a little back and then down and in. If done correctly, the shoulders should comfortably stay in place without any effort. It's like the shoulder are on a gear mechanism and they've been ratcheted back one location. You're not using the back muscles to hold them back. If you just use your back muscles to squeeze the shoulder blades together (as is done when you're told to "stand up straight") you'll feel your rib cage pop out and up; this creates a sway. The shoulders should be down and back while the ribs cage is also anchored down and back. Initially this may feel like you're leaning forward if you're used to being arched back with a sway. Look at a mirror to your side and you may be surprised to see you don't look as forward as you feel.
Next imagine you're grabbing a pony tail at the base of your skull and you pull it up and back. This elongates the back of the neck and moves the head back and over the spine. Now look at your side view in a mirror again. If you still notice a slight forward lean in the body, don't try to correct it by straightening up. Instead, keep the alignment in your spine with your ribs anchored and further tighten your abs. Imagine someone pushing straight back on your stomach (same horizontal direction as the floor) so that your upper body slides back over the hips (the upper back is still long like you're trying to get your chest over that imaginary bar).
If you get it right your spine will take more of a J shape than an S shape. Look for a long, straight back with an even groove along the spine and a curve at the top of the butt (at L5-S1). There are some fabulous images in Esther's book and on her web site that help to illustrate this.
http://egwellness.com Here are a few to help give you the idea.
This is Esther. Note how she is sitting with her tail behind her. Her back and neck are long, her shoulders are back and there is no sway in the lumbar area. Here she is demonstrating hip hinging. Notice how she leans forward by hinging at the hips instead of rounding the back. When she sits back up straight she keeps the exact same alignment from the neck to the hips and just rotates in the hip socket.
I hope this image of Ubong tribal people isn't considered inappropriate here. These folks spend a lot of time walking and running barefoot. Notice the even groove in the spine from the neck to the top of the butt with a curve at L5-S1. The spine is more J shaped than S shaped.
We all started out with the right posture and alignment. Babies the world over initially sit and stand with the posture alignment Esther teaches. Over time, due to a variety of cultural influences, many of us in industrialized areas forget this primal wisdom and take on a posture that causes us problems.
Peace,
Karen