Spanish Nights is an entry level tremolo study. It will sound good anywhere within the range of andante. This is absolutely the best piece ever written for getting started with tremolo, bar none, and you know how modest I am. ☺
The right hand fingering is “tami”. At some stage of learning tremolo, as a temporary measure, it may help to emphasize the middle note, played with the middle finger.
Practice this until you can play it smoothly and evenly at a variety of tempos. Keep it in the andante range according to your metronome. This piece actually sounds best if the tremolo is not nearly as fast as that required to make Recuerdos de la Alhambra sound good, for example.
For future reference, triplet tremolo is “tmi”, regular “classical” tremolo is “tami”, and flamenco (quintuplet) tremolo is “tiami”. If you use those fingerings consistently, it becomes very easy to change from one type of tremolo to another on the fly at tempo, because you can remember the sequence by remembering which finger immediately follows the thumb.