Rav Moshe writes that one should only wrap his Tefillin Shel Yad around his arm 3-4 times before moving on to putting on his Tefillin Shel Rosh, only afterward should be complete wrapping it around his. This is in order to avoid the unnecessary Hefsek.
Also note the unique minhag of reciting each word of the pasuk Poseach Es Yadecha as he wraps each round.
Published with permission from MD Yarmish.
