Wordpress - How do I query a custom post type with a custom taxonomy?

Firs of all don't use query_posts() ever, read more about it here: When should you use WP_Query vs query_posts() vs get_posts()?.

You have to use WP_Query to fetch posts what you need. Read documentation for it. In your case the query could be like this:

$the_query = new WP_Query( array(
    'post_type' => 'Adverts',
    'tax_query' => array(
        array (
            'taxonomy' => 'advert_tag',
            'field' => 'slug',
            'terms' => 'politics',
        )
    ),
) );

while ( $the_query->have_posts() ) :
    $the_query->the_post();
    // Show Posts ...
endwhile;

/* Restore original Post Data 
 * NB: Because we are using new WP_Query we aren't stomping on the 
 * original $wp_query and it does not need to be reset.
*/
wp_reset_postdata();

i am using this query to fetch custom posts (FAQs Posts) with its custom taxonomy (faq_category). since {taxonomy} parameter in WP_Query args was deprecated since v.3.1 and introduced {tax_query}. below is the code that works perfectly.

$query = new WP_Query( array(
    'post_type' => 'faqs',          // name of post type.
    'tax_query' => array(
        array(
            'taxonomy' => 'faq_category',   // taxonomy name
            'field' => 'term_id',           // term_id, slug or name
            'terms' => 48,                  // term id, term slug or term name
        )
    )
) );

while ( $query->have_posts() ) : $query->the_post();
    // do stuff here....
endwhile;

/**
 * reset the orignal query
 * we should use this to reset wp_query
 */
wp_reset_query();

Here the code that works like magic. I am fetching all posts for the custom post_type "university_unit" with custom taxonomy "unit_type" and multiple taxonomy terms as "directorate" and "office". I hope it helps out.

<?php
$args = array(
    'post_type' => 'university_unit',
    'posts_per_page' => -1,
    'orderby' => 'title',
    'order' => 'ASC',
    'tax_query' => array(

        array(
            'taxonomy' => 'unit_type',
            'field' => 'slug',
            'terms' => array('directorate', 'office')
        )

    )
);

$Query = new WP_Query($args);
if($Query -> have_posts()):

    while($Query -> have_posts()):
        $Query -> the_post();
        ?>
        <div class="cm-post-list-item">
            <article>
                <div class="cm-post-head">
                    <h3 class="cm-text-blue">
                        <a href="<?php the_permalink(); ?>"><?php the_title();?></a>
                    </h3>
                </div>
                <div class="cm-post-body"><?php the_excerpt();?></div>
            </article>
        </div>
        <?php
    endwhile;

else:
    "No Administrative Offices Found. Try again later";
endif;
wp_reset_postdata();
?>