For example, in 3/8 meter you can't create eighth note triplets (because that's the beat value). But you can create sixteenth note triplets very easily.
Today's piece for sight-reading is the Fugue in D minor by Wilhelm Friedemann Bach (1710-1784), J.S. Bach's eldest son which features sixteenth-note triplets in 3/8 meter.
Here is the score (p. 7) for you. The challenge lies not only in playing triplets but also regular sixteenths which come after the triplets. Do not rush the regular sixteenths. Count out loud the beats, if you need to keep the steady pulse.