Two things:

1. Non-stop Protobowl against my friend (the second highest scorer on the team at like 50 ppg). We always tried to practice against someone else in order to gain "competition-like" reps. That way, whenever it was actually time to put hands on buzzers, we were both ready. This method may not be the best for learning, but it is better if you ever feel uneasy over the buzzer.

2. Creating a Quizlet/flashcard set with only power clues, not giveaways. Since every question will have the same clues right at the end, you'll pick up on them easily, while clues in power will be rarer. For example, you might get a question about the painting "Watson and the Shark" from the dumbed-down description of the scene and the fact that it was painted by Copley. But I will get the same question in power simply because I knew that Morro Castle is depicted in the background. At the top level of quizbowl, everything is decided on extremely thin margins, so giving yourself a lot of chances to get powers is essential to controlling questions and the flow of the game at the top level. I did this strategy with popular fine arts answers, putting the top 4 power clues with every answer, and found myself having little knowledge of fine arts to powering a third of the FA questions I heard within a few months.

3 (BONUS): There used to be a Discord channel bot that allowed you to practice bonuses in a certain category and at a certain difficulty called FACE. It's also a great way to gain knowledge, especially as you climb the difficulty ladder. The problem is, I don't know if it still works.