A compás or two of Soleares, back in the beginning, when I thought I was a flamenco player (I wasn't). Then, my first actually decent guitar teacher gave me as an exercise, a few bars of what I subsequently discovered to be the beginning of Carcassi's 7th etude, and I was onto a path more typical of those already recounted in this thread. A suggestion was made as to your first essaying as an introduction to the technique, a tremolo piece with most of its emphasis on first string tremolo. This is a valid pedogogical thought, though the flip side of it may be that that would serve to ensconce the active technical interfaces that can make tremolo more difficult when moved to inner strings. Anyway, if this first foray is to be a significant piece with lasting place in your repertoire, then Una Limosna would fit this profile. The left hand demands really aren't that difficult, if one uses amenable fingerings, which aren't always those found in printed editions.