So, I upped pretty much all of my weights by 2lb yesterday, and I decided to ignore the weight suggested by the guy at Greens who set up my program and push myself up from a 20kg squat to 30kg (~66lb, for the imperials) and I'm now finding my final set of each exercise much more challenging, some of them even going to failure (not the squats, fortunately) :V
On my way home from the gym today, I got back on my bike after stopping at the supermarket, and felt my back muscles push my ribs and spine into place - as if my muscles are starting to support my skeleton, instead of the other way around. This pleases me immensely.
I've also been making an effort to keep my shoulders back and engaged, my feet aligned forward under my shoulders, and my head up instead of forward. It's tough training yourself out of lifelong habits, but I think it will be worth it.