Common mistakes in trading strategies include the lack of a clear plan, trading without proper risk management, over-leveraging, and being driven by emotions. Many traders ignore the importance of backtesting, entering the market without testing their strategy. Another frequent mistake is constantly changing methods without allowing time to evaluate results. Also, blindly trusting signals or indicators without understanding their logic can lead to wrong decisions. Furthermore, not following the established plan out of fear or greed, or failing to adapt to changes in the market, can result in consistent losses and frustration.