Travis Sawchik at 538 discusses how Cody Bellinger went about improving his swing. I especially like this drill he performed with Justin Turner on curveballs:

Bellinger’s interest in new ideas was piqued in 2017, when the lefty slugger was having a hard time hitting breaking balls. Turner — whose swing was revamped by Doug Latta, another outside instructor who had worked with Wallenbrock — took him aside in the Dodgers’ batting cages and challenged him to try to swing and miss under breaking balls off the slider machine. Bellinger couldn’t. They competed to see who could most often hit the top of the batting cage netting.

“You want to hit a curveball on the bottom part of the ball — it was practicing that every day,” Bellinger said last season. “We started in May and June and did it through the whole year. … Baseball is a crazy sport where it can just one thing for it to click,” he said.

Did that work pay off? Bellinger is hitting .462 on curves this season.

FiveThirtyEight.com

There are also very nice graphics of how Bellinger compares to the league in strikeouts, isolated power, and pop ups.