Here is an interview with trout. He probably is not 100 percent honest and I'm sure there are occasions where he sits off speed but I would assume that he is generally telling the truth.
What is extremely important is to have a yes yes no approach. Some people say look for a pitch in your spot and swing but that is bad, you want to think swing first and then stop if it is not a good pitch to hit.
Practice active takes. I like to have them do what I call early check swings which means stopping the bat about in the 45 degree position (see picture). Alternate pitches in the dirt and middle middle and have him stop in the early check in the bouncers and actually swing on the middle ones but time up every load for a fastball in the zone.this will give him much more time to read the pitch. Progression is first do early checks on pitches down the pipe so you stop when ball is about 2/3rd home, second you alternate between check and swing and third is random bounced and in zone balls.
