When I first started in design, I often made classic mistakes: overloading the interface with elements, making unreadable fonts, and not considering color combinations. One of the most memorable failures was related to the poor choice of buttons: they were simply lost in the background. Over time, I realized that the best solution is simplification and testing. I highly recommend reading Conversion Rate Killers: Design Mistakes. This article helps you see typical mistakes through the eyes of the user. For example, excessive pop-ups or complex registration forms are very off-putting.