How can i get customer data from observer after successful login?

Use the event customer_login:

<customer_login>
    <observers>
        <yourobservername>
            <type>model</type>
            <class>yourmodule/path_to_class</class>
            <method>customerLogin</method>
        </yourobservername>
    </observers>
</customer_login>

Your observer class would look like this:

class YourCompany_YourModule_Model_Observer
{
    public function customerLogin($observer)
    {
        $customer = $observer->getCustomer();
    }
}