1)  Originality – Traders who develop their own, unique approach to markets are more likely to succeed that traders that employ generic methods.  My common impression when I meet a promising trader is, “Wow…why didn’t I think of that?”  I quickly recognize that the trader has achieved an insight that others have not.  That original thinking is more likely to generate distinctive results than run-of-the-mill thinking you could hear from any of a dozen market participants.
2)  Flexibility – The worst traders I know are perma-bulls or perma-bears.  They fit markets to their own thinking, rather than adapt to changing markets.  The best traders work with a kind of anti-confirmation bias:  they actively scan for information that does not fit with their views.  That enables them to be flexible and adapt quickly to new market conditions.    
If I were to place these two predictors of success under one umbrella, it would be “real-time creativity.”  The successful trader sees and approaches markets in fresh ways–and continually refreshes those perceptions and methods.