As sergeant major of the army, Preston served as the army chief of staff's personal adviser on all [soldier]-related matters, particularly in all areas affecting soldier manning, equipping, training, education and quality of life.
His military education includes Basic Noncommissioned Officer's Course, Advanced Noncommissioned Officer's Course, First Sergeant's Course, M1/M1A1 Tank Master Gunner Course, Master Fitness Trainer Course, Battle Staff Noncommissioned Officer's Course, and the United States Army Sergeants Major Academy.