"and it shall be to you as a sign upon your hand and as a memorial between your eyes": When the hand tefillin are on your hand, place the head tefillin on your head — whence they ruled: The mitzvah of tefillin: When he puts them on, he puts on the hand tefillin and then the head tefillin. When he takes them off, he takes off the head tefillin and then the hand tefillin.
The Exact Order for Putting On and Taking Off Tefillin
Mekhilta Tractate Pischa 17:28