You need to be more stubborn than the horse. My horse used to be very stubborn - and in some ways he still is.
Groundwork him more before you place the saddle on, then groundwork him more after the saddle is on.
You need to teach more ground manners and get big when you need to.
My horse doesn't like the bit being put in because he knows it means he will have to work. Some days he will actually put it in there for me if he had a good ride before today, but if he wasn't too happy or just doesn't want to work today then he will shoot his nose into the air. So I grab hold of his halter and hold one side of the bit in one hand, to keep him head down. And with my other hand I put it right in front of his mouth and stick my finger in and make him uncomfortable. It usually works pretty well.... after a little fuss.
But overall in my year of working and riding with brisco, he has gone from pushy, mean, grumpy, bossy, tough, and stubborn horse to a happy, still a bit stubborn, following, companion. He does what I ask of him whether he wants to do it or not, and he no longer does his little mini rears and spins.
Brisco and I have gone and accomplished so much in a year that if I was told that today I would be barrel racing, parade riding, trail riding, and transforming brisco into a completely new horse and having changed myself in the process, I would have pushed them off a bridge for thinking of such an impossible thing. I would have not believed them one bit.
Bit one thing that did help me get here, was be more stubborn than the horse, get big right as he comes to nip you, and if he did something wrong or bad, correct him and teach him that wasn't any good.
In the process I built up my confidence so much - I am not even shy around people now I just jump right in and say hello. Yes, horses DO help you when you aren't even with them.
🔫 Don't Tread On Me 🐍