add_filter('woocommerce_checkout_fields','reorder_woo_fields');

function reorder_woo_fields($fields) {
    //move these around in the order you'd like
    $fields2['billing']['billing_first_name'] = $fields['billing']['billing_first_name'];
    $fields2['billing']['billing_last_name'] = $fields['billing']['billing_last_name'];
    $fields2['billing']['billing_company'] = $fields['billing']['billing_company'];
    $fields2['billing']['billing_address_1'] = $fields['billing']['billing_address_1'];
    $fields2['billing']['billing_address_2'] = $fields['billing']['billing_address_2'];
    $fields2['billing']['billing_city'] = $fields['billing']['billing_city'];
    $fields2['billing']['billing_postcode'] = $fields['billing']['billing_postcode'];
    $fields2['billing']['billing_country'] = $fields['billing']['billing_country'];
    $fields2['billing']['billing_state'] = $fields['billing']['billing_state'];
    $fields2['billing']['billing_email'] = $fields['billing']['billing_email'];
    $fields2['billing']['billing_phone'] = $fields['billing']['billing_phone'];

    //just copying these (keeps the standard order)
    $fields2['shipping'] = $fields['shipping'];
    $fields2['account'] = $fields['account'];
    $fields2['order'] = $fields['order'];

    return $fields2;
}