One aspect that confuses and is a lesson often learned the hard way .. is the understanding of fabric grain and how and when its important.
The other issue I see with beginners is color... They finish a quilt but wonder why theirs does not have the "zip" of what they see either hanging in the shop , magazines, shows etc. It was a HUGE light bulb moment for me in my quilting journey after attending International , was color and using it effectively.