Finding a profitable trading strategy is not easy, traders need the discipline to walk strategy to measure performance trading strategy, greedy or overtrading is one thing should be avoided by beginner trader.
I can think of a lot. Don’t open an account with the wrong broker, don’t start trading without a proper education, trading with no demo experience, not using proper risk management, using too high leverage, deviating from your strategy, and so on.
A trader should never put his whole deposit in risk in one single trade. Many newbies have such a temtation when they are overconfident, but such an action will definetely result in the absolute loss of the money sooner or later.