I think PrepExpert has really helpful strategies all explained in their books that helped me raise my score by 150 points. Regarding teachers, I first had Justin Tandon who seemed kinda lost or unsure on how to solve a problem and I felt like my time was being wasted when he would explain relevant strategies that were time consuming. Half way through the course my new instructor was Pranav Samineni who was much more helpful regarding how to approach and solve a problem the fastest. But to improve your score the strategies are more helpful and beneficial than anything an instructor and provide.