One advice I can give you is with time and more practice it will feel second nature. Once that happens you will be more consistent and will be stressed less. When you are relaxed you won't physically or mentally get tired so easily.
If you're stressed your body tenses up and you become worn out much sooner.
2013 E92 ///M3 Space Grey w/ Fox Red
M Performance Exhaust, KW Sleeve Over Kit, and cosmetic upgrades