Elvis said in many interviews that he tuned his voice everyday. His high quality vibrato shows that he practiced that also when he tuned his voice. Everyday he would play the piano and sing.
Elvis never drank alcohol. Alcohol affects your ability to sing well. You should not drink if you want to sing at a professional level and definitely not drink on the day, or even the day before, of a performance. If you did drink some alcohol, exercise it out of your system as soon as you can.
Many writings talk about how Elvis exercised constantly. He rode a stationary bike. He practiced Karate.
In the 70’s he started playing racquetball with the “Memphis Mob.” He started playing at the local Y and at Memphis State. His two favorite things to do was go to the movies and play racquetball. In the summer of 1975, Elvis decided to bring his racquetball hobby closer to home. He began planning to build a racquetball court at Graceland, and construction of the building began in September 1975.