Here comes the 18th Study by M. Carcassi for triplets.
Playing triplets evenly might be difficult for some people. Here, you will see triplets in different textures, such as scales, arpeggios, repeated notes, high notes, low notes and so on.
In order to get used to triplets, you should start slowly counting 1, 2, 3, 1, 2, 3. The variations of texture patterns will keep you interested during this kind of slow practice.