Guaracha is the fast, joking member of the son family — the 19th-century theatre song that became, through Beny Moré and the Sonora Matancera, the up-tempo dance number of every conjunto. Same clave, same tumbao as son montuno, just quicker and lighter.
How it sits: 2-3 son clave. The piano guajeo plays block triads with the top note doubled in the left hand, on the son montuno rhythm: down on 1 in the 2-side bar, all offbeats in the 3-side. Every chord change is anticipated by an eighth — G7 arrives on the and-of-4, the return to C on the last eighth. The bass is the anticipated tumbao: and-of-2 and 4, each note the root of the chord that is coming, never the one that is sounding.
Listen for the bass and the piano both arriving early; the downbeat of the 3-side bar is the only place nothing new happens.
Practice: start at 150 and push up only while the anticipations stay ahead of the beat, not on it.