Join Date: Jun 2017
Location: middle of nowhere
Enough so there's no pressure on the bit when the horse is moving normally, but you can take up the slack to get a response without moving your hand/arm a whole lot. For just pleasure riding, do what works for you. In the show ring, it's common to 'pitch the reins' (ride with a huge amount of drape) to show the horse is moving on his own with no cues. If you're showing and your horse isn't ready for that yet, then you do what you need to do to maintain control. Bear in mind that most of those show horses with a huge rein drape are also trained with a spur stop, rather than a rein cue, to slow down or stop.
If you have to move your arm up to your chest (or above your head... don't laugh, seen it) you have too much slack.