Email First in WooCommerce Checkout

woo-checkout-email-first.php

<?php

// make email the first field on the WooCommerce checkout page
add_filter( 'woocommerce_checkout_fields', 'sb_edit_checkout_fields' );

function sb_edit_checkout_fields( $fields ) {

    // make email first
    $fields['billing']['billing_email']['priority'] = 4;
    return $fields;

}