Patience, hard work, dedication, grit and a lot of natural talent - feel.
Money will help a heck of a lot - to pay for lessons and clinics with top coaches. Without a very good coach, you won't learn enough to become a top rider yourself.
It takes a very long time, and there are thousands of riders out there who have all of the above, and are still not classified as 'top riders', only 'good riders'.
You'll need to ride as many horses as you can, spend a lot of hours in the saddle, develop an immaculate seat and don't go and have a cry if you get yelled at. You WILL get yelled at, screamed at, told you're useless, etc. if you start having lessons with top level coaches.
I've been chased around the arena with a lunge whip, had welts on my leg from being hit with a dressage whip when I wasn't using enough leg, had my hands strapped to the saddle cloth, been made to ride one of my head case horses with no stirrups and reins - not on the lunge! I've been told that I'm too short, too stumpy, my chest is too big!!!! I don't have enough money, I'm in the wrong state of the wrong country.... it goes on.
You need a VERY tough hide if you want to ride with these tough coaches. If you can grit your teeth, listen to them, and use the anger you feel in a positive manner "I'll show you!!!!" then you will improve in leaps and bounds.
The money is hard, you will need to make many, many sacrifices to afford to continue on this path. I have a clinic with a national level Grand Prix rider coming up this weekend. I am paying in the mid-high hundreds per lesson, for 40 minutes. That is on the lower scale of clinic fees.