Boring gym post|
On the back/shoulders/head alignment, there're various techniques i've been shown with drama to help, such as standing straight and then imagining you're dangling from a piece of string attatched to the crown of your head - that straightens everything and helps you know how it feels when your head is up (i have the same problem). Alternatively, lie on your back on the floor, feet flat, knees bent, head raised by a couple of inches (no more) and then rest your hands by your side or in your stomach and just lie like that for 10min a day - again lets the spine fall into place.
I've heard the head/string thing a lot, but really my muscles are trained to hold my head forward far too well, and I'm going to have to train myself out of it gradually.
The floor exercise sounds pretty useful - it sounds like it trains your muscles to support your head in a different position.