At a certain time, I liked to play a tremolo piece. The problem with the standard tremolo pieces (like Recuerdos de la Alhambra by Tarrega) is that you need quite some skill and condition before you can play the tremolo smoothly.
My teacher Robert Horna had a nice old Polish music book in which we found a short but effective tremolo piece. The piece appeared to be fun to play and offers a nice practice for tremolo technique. It is a variation in tremolo on an Italian folk song, composed or arranged by Luigi Mozzani.