How to correctly pass values to wpdb->prepare()?

I’ve found an answer by myself..

(sample code)

$args_array = array($post_type);
$term_slugs = array('foto', 'video');

// create a string like '%s, %s' ecc
$placeholders = implode(', ', array_fill(0, count($term_slugs), "%s"));
$term_query = "t.slug IN ($placeholders) ";
$args_array = array_merge($args_array, $term_slugs);

$ids = $wpdb->get_results($wpdb->prepare("
  SELECT
    m.meta_value
  FROM
    " . $wpdb->prefix . "posts p
    INNER JOIN " . $wpdb->prefix . "postmeta m ON m.post_id = p.ID
    INNER JOIN " . $wpdb->prefix . "term_relationships rel ON p.ID = rel.object_id
    INNER JOIN " . $wpdb->prefix . "term_taxonomy tt ON tt.term_taxonomy_id = rel.term_taxonomy_id
    INNER JOIN " . $wpdb->prefix . "terms t ON tt.term_id = t.term_id
  WHERE
    p.post_type="%s"
    AND m.meta_key = '_thumbnail_id'
    AND p.post_status="publish"
    AND $term_query
  ORDER BY RAND()
  LIMIT 1
",
$args_array // pass substitutions as an array
));