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Perhaps you've worked on Wagner's Ride of the Valkyries. This excerpt poses many lovely challenges. One of them: make sure the pickup notes are triplets.
A recent lesson: a student couldn't get the triplet feel. With the metronome running, I asked him to play the Mexican hat dance. BOOM! the triplet troubles vanish.
Old theme: relate to the familar!
Metronome still running, I ask him to start out with mexican hat dance and then transition smoothly into Valkyries. Like this:
No triplet troubles on hat dance BUT as soon as he switches to "Valkyrie Mode" the triplet feel is lost.