Your sentence has excellent ideas! I hope I have properly understood your thoughts. I think by simplifying the sentence and dividing it into two points, you can give your ideas more power. Here is one way to do that. By listening to the experiences that my teacher shared during class, I realized something very important! Memorizing and simply reciting others' so-called perfect answers will not improve my understanding of English, neither will it lead to higher IELTS exam scores. The first sentence deals with WHERE you were. The second sentence deals with WHAT you learnt. I hope this gives you some ideas.

'From my experiences as a student and from hearing my teacher's own experiences, I realized that memorizing and reciting textbook-perfect answers weren't the best ways to improve English speaking skills and achieve my best in the IELTS exam.' Due to~ Makes sense, but is best used in serious cases or when there is a negative result. The comma I placed seperated two bodies/clauses of the sentence made it slightly more organised. Worst and most terrible -> they imply the same thing and "worst" would be the better of the two, "most terrible" sounds a little dramatic. I've changed "worst" to "wasn't the best" because I feel that worst makes it sound too serious and "wasn't the best" is a very easy-going expression. Good luck with your studies :)