The tefillin should be placed on one’s arm opposite their heart and near their brain, to remind us to direct all of our actions and thoughts to serve Hashem. One should have in mind that Hashem should help us lessen our desires in this world, and protect us from seeking after our heart and eyes in the wrong way. The shel yad be placed on the lower half of where the muscle is puffy and tilted a little towards the heart. The shel rosh should be put in the middle of the head and not lower then the hair line. The knot in the back of the head must be by the dent.