I read this hint somewhere, and I just love it for the arm-position thing: hold the bar like it's bigger around than it is. (so keep your hand a bit more open, but not loose or sloppy)

I've only had the chance to try it once so far, but that one cue seems to tie in core/spine posture/arms/elbows/shoulders for me. And I liked it even more than the "playing piano" cue.

It's very hard to ride with too much weight on the bars if you are holding your hands a bit more open. I could really feel it in my core, so I'm guessing that's my weak spot.