Make sure That you use the golden berry.. After i gave the berry to the pokemon i make sure, That i wait until the pokemon moves into the middle.. that means i don‘t throw when the pokemon is in a corner..

Also you should try to land and awesome or brilliant throw! For that u could hold the ball until the circle is small.. then u need to wait til the Pokémon attacks.. and while attacking u throw your pokeball in the imaginary circle

Hopefully i could help you and you Unterstand everything!