Resaltan means 'they stand out' or 'they are highlighted'. It's a descriptive verb that adds a touch of elegance when describing features.
In the song, Lucky Brown uses it to paint a vivid picture of the woman he's captivated by: "De piel canela y sus ojos resaltan" (With cinnamon skin and her eyes stand out). This word beautifully emphasizes her striking beauty, making her eyes the focal point and creating a memorable image for the listener.
In "Avísame," Lucky Brown is completely fixated on a woman after one incredible night together. He's not subtle about it at all. He's asking her to just give him a sign, singing, "Avísame si tú quieres volver... Que yo estoy loco por volverte a ver" (Let me know if you want to come back... 'cause I'm crazy to see you again). The whole song is basically him replaying their time together in his head and hoping she'll call.
He remembers every detail, from her looks—"Una peli negra de estatura alta / De piel canela" (A tall, black-haired girl / With cinnamon skin)—to the more... intimate moments. He's so obsessed that he admits, "Estoy volviéndome loco yo / Ya no puedo contenerme / Cuando veo tus fotos yo" (I'm going crazy / I can't contain myself anymore / When I see your photos). He thinks she's into a specific type of guy, the "shoros, los gangster" (tough guys, the gangsters), and he presents himself as that kind of young guy from "the trap."