Before we get too deep into the heavier triplet-slash-12/8 stuff, here's a page of basic grooves. Gotta make sure everyone is taken care of. 12/8 is a compound meter (meaning it has a “triplet” feel— each beat is divided into three notes rather than the usual two), and is counted in 4— don't count it in 12. If you played a measure of 8th note triplets in 4/4, you'd have basically the same thing, for all practical purposes. Here I've written a number of grooves with running 8th notes on the hihat, and some with a shuffle rhythm.
Play these many times each, until you relax and your hands and feet begin to know what to expect. Then start memorizing the grooves, or more importantly, the things that happen during them: What kinds of things happen at the beginning at the measure, going into the first snare hit? What happens between the two snare hits? What happens at the end, going into the 1? Begin improvising new, varying grooves by playing with those things, switching them around on the fly as you recall them.
From last year, this page of “studio triplet” grooves/ideas is a good companion to this page.
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