Poseiach Es Yadecha:
The meaning: The verse of Poseiach Es Yadecha is a praise to Hashem for supervising His creations and providing them with sustenance. [In Chassidus, it is explained that this verse is a request from Hashem to enter into one’s heart His Divine will and desire to be King over him.]
Concentration: One must [especially] concentrate upon saying the words Poseiach Es Yadecha, on the meaning of the words that he is saying. [One is to also concentrate on that the Roshei Teves of the words spell the Divine name פא”י and is the Gematria of the names Havayah and Adniy. Likewise, one is to concentrate that its Sof Teveis spell out the word Chatach, which is the Divine name authorized over the giving of Parnasa. One is however not to concentrate on the deeper Kabalistic intents unless he is holding on the proper level to do so.]
One must especially concentrate upon saying the words Poseiach Es Yadecha, on the meaning of the words that he is saying.
Touching Shel Yad and Shel Rosh:
Some are accustomed to touch the Tefillin Shel Yad upon saying the words Poseiach Es Yadecha and to touch the Tefillin Shel Rosh upon saying the words Umasbia Lechol Chaiy Ratzon. This is the Chabad custom. Some however are accustomed to touch the Tefillin with the straps and not directly with their hands.
Raising the eyes towards Heaven:
Some are accustomed to raise the eyes upon saying the verse of Poseiach Es Yadecha.
Raising the hands:
Some Sefaradic communities have the custom to open the hands towards Heaven upon saying the words Poseiach Es Yadecha. [This is not the Chabad custom.] One who follows this custom is to beware not to lift the hands above one’s head.
Some are accustomed to distributing charity upon saying the verse of Poseiach Es Yadecha. [This is not the Chabad custom.]
 Admur 51:8; Tur 51; See Piskeiy Teshuvos 51 footnote 141 for various explanations of the word Ratzon
 See Likkutei Torah 54a
 Admur 51:8; Michaber 51:7; Rabbeinu Yonah Brachos 32a in name of Gaonim
 This is in addition to the generally required concentration upon saying the Psalm of Tehila Ledavid, as one merits Olam Haba with the recital of this Psalm. Nevertheless, upon saying the verse of Poseiach Es Yadecha one must add in even more concentration. [Tur 51; Levush 51:8]
 Kaf Hachaim 51:34; Piskeiy Teshuvos 51:17
 Kaf Hachaim ibid; Chayeh Adam 18:2; However see Ben Ish Chaiy Vayigash 12
 Taamei Haminhagim Likkutim 177
 The reason: This is to emphasize that the reason for why we ask for Parnasa is so we can perform Hashem’s Mitzvos. [ibid]
 Igros Kodesh 18:265; Sefer Haminhagim p. 9 [English edition p. 22]
 Igros Kodesh ibid
 Sefer Chareidim chapter 4
 Ben Ish Chaiy Vayigash 12; Torah Leshma 31; Makor Chaim of Chavos Yair 51:7
 The reason: This is done in order to make a physical vessel for the blessing. [ibid]
 Ben Ish Chaiy ibid
The reason: As according to Kabala one is never tor aise his hands above his head with exception to Netilas Yadayom and Nesias Kapayim. [Ben Ish Chaiy ibid]
Other opinions: Some Poskim rule one is to raise the hands above his head when reciting Poseaich Es Yadecha. [Yad Yosef p. 15, brought in Ben Ish Chaiy ibid]
 Likkutei Maharich in name of Seder Hayom and Mavor Yabok