Visit the Alhambra museums during your Nasrid Palaces slot
When Alhambra visitors hold timed entry windows for the Nasrid Palaces (typically 08:30 to 14:00), the two museums in the Palacio de Carlos V are at their quietest. Go to the Museo de la Alhambra during the morning entry rush and you'll have the galleries largely to yourself. The inverse is also useful: if you hold an afternoon palace slot, arrive early and spend the first hour in the museum before your timed entry begins.