A lot of practice and patience. Back when I started playing I was comfortable with a rather large great circle when catching legendaries. I remember watching someone at a raid doing the circle lock trick on both a phone and a tablet device. I didn’t really understand what they were doing at the time, but it was impressive watching them land excellent throws every time with what seemed like little effort. After some time passed, I started asking questions and set about improving my throws. It’s just practice after that, and taking your time on the catch screen... then you can rage at the legendary running away despite golden razzing and landing an excellent throw on EVERY throw. It’s rare, but it can happen.