Here's a tip if you have the habit of sitting with your legs crossed. Get an ankle bracelet. Get one with lots of bits dangling from it like a charm bracelet or with big beads. Cross your legs and the bracelet will dig into your other leg, making you uncross them!

(Incidentally, this also works with wrists if you have the habit of resting them on the keyboard/desk. Big chunky bracelets or leather strips with big press studs do the best job).

LTS