I've never had a problem with heart gesture but I get lulz from your suffering. :laugh2 I start at the point, and just... Draw a heart.
My advice: Take up Wicca. Not really, but it helped me. You get a steady hand from moving heavy things around in complicated patterns after a while, so taking up swordplay would likely also help. Also, you can trace the gestures pretty slowly, so focus on accuracy before speed, and "M" skips the miracle selection stage, "R" repeats your last miracle. Most of the miracles don't have exact gestures; Circling a few times does a spiral, going generally up and down makes a fireball/leash of aggression, lightning can be done by going over the first and last lines twice, and the teleport is not that hard to hit; Make a quick vertical motion with the mouse, a quick diagonal up, and so forth. It doesn't have to be one fluid motion. And I hate to say it, but trackballs and touchpads are better for gestures if you have an unsteady mouse hand.