The most direct answer to this question would be through a lot of hard work. My best advice would be to take advantage of every free learning opportunity, whether it be auditing a clinic, watching a Grand Prix or just sitting and watching the warm up ring at a show. You can learn so much just by watching top riders warm up their horses and even by watching how they warm up and train their students.
Along with watching, try your best to align yourself with the right people. Try becoming a working student to learn how a top program and top horses are managed. You can take away so much valuable knowledge from those experiences that you one day can apply to your own business as a professional.
It does take a lot of work to make it without support, but it is completely possible! Kent is a great example of this; he didn't start out with a big pocket book supporting him. He aligned himself with the right professionals and worked his way up to the rider he is today.