You must start by having sponsors, so brands will know you and give you equipment and make some publicity for you.
Actually it is hard to break through the equestrian world. When you want to become a famous rider or jockey, you need to be better than others.
Will and Ryan are right. Unfortunately, a lot of young riders dream of becoming a famous rider but it is really hard. If your parents have good relations in the equestrian milieu, it can be easier. But it costs a lot of money and take all your time. You have to be ready for this way of life!
I agree with Will. A lot of riders want to become a professional rider but only a very few of them succeed in becoming one! It is really hard.
I am not gonna lie, it is hard. You have to train a lot. Find stables where you can ride prestigious horses, do a lot of competitions, try to have a lot of relations. You also need to have enough money to afford everything as it is a very irregular profession, you can win money in a show and then nothing during 2 months!!