Slight pressure on the reins- outside, inside, outside. Keep asking with your calves to avoid breaking. If that’s not helping, I suggest doing both of those and switching the bend. Have Ann outside bend for half a lap, stay straight for half, inside bend, to straight, to out so on and so forth. I know it sounds complicated, and I suppose it is, so the best thing to do is keep practicing! Watching YouTube videos helped me as well. Good luck! You got this
Well Karina, not every horse that is stubborn is tired or doesn't understand. At some point or another every horse will have days where they don't want to listen and do what they're asked. And I'm not saying that the horse I'd being naughty either.
To be fair, you've also asked how to do sitting trot and said you haven't cantered yet. Collection is the last stage in the scale of training, and something even intermediate riders struggle to understand and do. I wouldn't worry about schooling a horse until you yourself have a solid understanding of the basics.
To achieve an actual collection with your horse you need to practice on rhythm, suppleness, connection, impulsion, straightness and then yoi can work on collection.
Any horse that is stubborn either is tired or don't understand what it's asked for. Horses don't tend to be naughty, they either understand or not. Also riding school horses tend to be stiffer, tired and have different riders that put their aids on differently and they need to adapt every time which can be exhausting as well.
If you've got your own horse that I ride regularly and no one else rides it, if you work on these things in this exact order you will soon be able to collect your horse.
This is how it's done in dressage and for example, you will never get connection without suppleness. If your horse is tense and not relaxed it won't be willing to cooperate and accept the bit.
All of the horses I've ridden have been really stubborn about collecting, so what I've done is I turning their head to the inside a little bit, and half halted on the outside rein, but keep slight pressure on the inside rein but not as much as the outside rein. But you also have to keep pressure on with your calves so they don't break down to a walk or slower gait than you're going. Sorry, it's kinda hard to explain but I hope this helped a little!