Young hitters improve fastest when they master a few basics instead of copying the swing of their favorite pro.
Stance and balance come first. Feet roughly shoulder-width apart, knees slightly bent, weight on the balls of the feet. A balanced hitter can adjust to pitches; an off-balance one cannot.
Next is a short, direct path to the ball. Tee work is the best way to groove this: place the tee in different spots for inside, middle, and outside pitches, and focus on hitting line drives rather than fly balls.
Finally, train the eyes. Ask hitters to say the color or number written on a ball as soon as they see it during soft-toss. Tracking the ball longer leads to better contact more than any mechanical tweak. Keep sessions short and frequent; fifteen focused minutes beats an hour of tired swings.