I never let a horse address a jump when they have refused. Unless it was the rider's fault (impossible distance, major steering fail, etc.), I'd tap hard with the crop behind my leg, and try again, unless the jump is small (up to about .75m with an average horse), in which case I'd jump it from a standstill. If I'm going to try again, rather than jump from a standstill, I make sure the horse is in front of my leg and straight on approach, in a forward, positive canter. If the horse is really backed off to the fence or sticky on takeoff, I'd use the crop again. Stopping can absolutely not be an option.
If a jump is potentially VERY spooky, I may give the horse a chance to get his eye on it before asking him to jump it, but like the poster above me said, I wouldn't ever walk him straight up to it and stop, I'd just ride past it and let the horse see it that way.
ETA: I'm imagining the horse stopping right in front of the jump. If she's running out, then that's really a steering problem. Make sure you can ride her straight, between your hand and leg. If she's trying to run out, you can't let her get past the jump ever, until she goes over it. She can't canter past the fence and then come back around and try again.
Last edited by KWPNowner; 07-21-2013 at 06:17 PM.