My issue with posture is my neck! This will sound strange, but my neck is quite long and so it's takes an effort for me to hold it straight, what with my heavy head on top of it. Don't worry, I'm not freakish looking (I don't think), and when I hold it up nice and straight, a long neck is quite elegant looking. But I still haven't gotten it into a permanent habit, since it takes that extra effort for me

When I do remember to lift my head up higher though, it's as if the rest of the back and my body does too. So maybe that's a good tip to start off with - lift your head!!
It's funny, my sister and I are the same height, but her shoulders are higher than mine. The only reason why I'm as tall as she is, is because of the extra cm. from my neck!
Anyone else have this wierd situation?
(<- maybe that's why I liked my avatar haha)