ACF – Theming Flexible Content

And to add to previous answers, you can not only use get_template_part, but also use it’s second param and combine it with ACFs get_row_layout.

So let’s say that somewhere in your template is:

<?php while ( have_posts() ) : the_post(); ?>
<article>
    ... SOME CODE

    <?php while ( have_rows( 'YOUR_FIELD_NAME' ) ) : the_row(); ?>
    ... HERE SHOULD GO THE CODE FOR ACF FIELD
    <?php endwhile; ?>

    ... SOME OTHER CODE
</article>
<?php endwhile; ?>

You can change it to:

<?php while ( have_posts() ) : the_post(); ?>
<article>
    ... SOME CODE

    <?php
        while ( have_rows( 'YOUR_FIELD_NAME' ) ) :
            the_row();
            get_template_part( 'block', get_row_layout() );

        endwhile;
    ?>

    ... SOME OTHER CODE
</article>
<?php endwhile; ?>

Then you can create your custom templates named: block.php (it will be used as fallback), block-layout_1.php (it will be used for layout called “layout_1”, and so on.