function validation(form) {
    if (form.first_name.value == '') {

        alert('Please enter your first name');
        form.first_name.focus();
        return false;
    }
    if (form.last_name.value == '') {

        alert('Please enter your last name');
        form.last_name.focus();
        return false;
    }
    if (form.email.value == '') {

        alert('Please enter your email address');
        form.email.focus();
        return false;
    }
    if (form.phone.value == '') {

        alert('Please enter your phone number');
        form.phone.focus();
        return false;
    }
    return true;
}