I agree with Nana-san. The literal translation of "my dream is to learn how to ride a horse very well" is わたしの夢はとてもじょうずに馬にのる方法を学ぶことです and the sentence of Nana-san's answer sounds more natural in Japanese.

Japanese say,わたしのゆめは、じょうばがうまくなることです。 ride a horse =じょうば jouba