Triplets are the question my students ask most. Three strokes where you are used to two, and the rhythm becomes flowing, almost hypnotic.
Honestly, triplets took me longer than anything else, until I understood one thing about a relaxed wrist. I show it here. Try it slowly: once it clicks, you will not want to stop.
Improvisation course: 18 short lessons, rock 3/4, eastern Talla 8/8, African 5/8. €35 a month with the first week free, or the whole course for €150.