Inside leg on the girth, outside leg behind the girth. Don't exaggerate it so much that you end up out of balance though. If you're working in the school it helps you get the correct lead if you ask going into a corner.
It really depends on the horse.
I've been riding a new horse in my lessons lately, and I'm still trying to find the right "buttons", but I cantered him on both leads during my last ride. Among other things, I sat up straight, sat back, threw my hips forward .. and thought 'canter'! I have a tendency to hunch/collapse forward which blocks the horse's movement as I then grip with my knees for balance, so remembering to sit up and back, and to really ride the canter when it comes are important points for me to remember.
The horse may well know what to do, particularly if the instructor is yelling 'canter'!
When asking for a canter from a walk is a lot of times easier as the cue can be easier to communicate. Outside leg goes back behind the girth a few inches and inside leg goes on. From a trot you sit (meaning if you were posting you stop and sit the trot), and outside leg behind the girth and inside leg at the girth. Staying tall and breathing will help and keep you from tensing up too much.Does anyone have advice on cantering? I have come back to horse riding and did this before but never knew how it happened. I remember something about leg back or leg on girth?