A significant amount of domain knowledge. You need a solid foundation in higher mathematics, statistics, and economics. This industry is extremely competitive and you'll quickly notice the manipulative games that are being played. If it were a simple technology game, a lot more market participants would be successful. That being said, as a retail trader, you have significant advantages, as far as capital allocation and risk tolerance. The best advice I can give you, look for edges were it would be impractical for the big boys to do so. Out of curiosity, what do you think is actually involved in quantitative trading? How do you think models are created and applied?

If you want to chat a bit more, let me know.