Learn the canter transition: use preparation, leg and weight aids to strike off on the correct lead, calmly and without rushing, with an instructor.
Why doesn't my horse strike off on the correct lead? The honest answer: usually it's not the horse but the preparation. Canter is a three-beat gait followed by a moment of suspension in which one front leg "leads", the right in right canter [1]. For your horse to strike off cleanly it needs a transition that is prepared, clear and calm.
The FEI rules describe the quality of the canter like this: it should arise light, even and without hesitation from the transition [1]. And every transition should be announced by an invisibly prepared half halt, an almost simultaneous action of seat, legs and hands that improves attention and balance [1]. That is the basis of clean striking off.
Why you should practise both sides: a study on ten ridden horses showed that the leading and trailing limbs work differently; the authors conclude that both canter leads should be trained equally to build symmetry and muscle strength [2]. If you only strike off on the "good" rein you load the horse one-sidedly.
A classification note: striking off does not belong in the very first riding lessons. Honestly rated it is intermediate, because you must first sit the trot securely before you can dose the aids finely.
Agree with your instructor which aid you give in which order. Practice standard: the inside hip goes slightly forward, the inside leg rests at the girth and drives, the outside leg rests about a hand's width behind it and stops the hindquarters swinging out. The hand allows a slight bend without pulling. Milestone: you can say the order aloud without thinking.
Before the transition a half halt: briefly seat and leg, take the hand lightly, then give again [1]. The trot becomes more active, not faster. Milestone: the horse trots evenly and stays on the rein.
Ride the transition where the horse is naturally bent: on a circle or at the end of a corner. This helps get the correct lead.
Give the aid in order: weight, inside leg drives, outside leg guards. Then give and let the hand follow. Canter is easier to sit than trot because the forces act more evenly [3]. Milestone: the horse strikes off from trot without rushing first.
Glance at the inside shoulder: if the inside front leg goes forward you are on the correct lead. If not, make a clean downward transition and start again.
Back to trot, praise, short break, then the same on the other rein. Practise both sides equally [2]. Milestone: you manage three clean transitions on each rein.
The transition into canter is a moment of increased dynamics: the horse accelerates and you lose balance easily. Practise it only with an instructor, in an enclosed arena and with a helmet. Helmets protect against skull fracture and severe brain injury; vests can protect the chest but not reliably the spine [4]. If the horse spooks or bolts: keep your seat deep, breathe calmly, shrink the circle and go to the full halt with a soft hand. Riding carries risks for humans and horses that also depend on training and aids [5]. This does not replace supervised training.
Before striking off, ride a circle in a very calm trot and shrink it slightly. The horse learns: when the hindquarters come under the body, the canter comes next. And you learn to put your aid at the end of the corner, exactly when it is easy for the horse.
You prepare the transition with a half halt, give the aid with inside hip, inside leg at the girth and outside leg behind it, then give. The FEI demands that the canter arises light and without hesitation [1].
In right canter the right front leg leads [1]. Glance at the inside shoulder: it should go forward. If in doubt, your instructor can tell from the ground.
Usually preparation is missing or the aid is combined with too much hand. Ride a half halt first, drive clearly and give as soon as the horse jumps.
Yes. The leading and trailing limbs work differently, so the authors recommend training both sides equally [2].
When rising and sitting trot are secure, the full halt works and your instructor approves. There is no fixed time window.
Riding the Canter: Swinging Along Loosely from the Hip