Q. Since the Halacha is that you need kavanah or intention to comply with a Torah mitzvah and according to some even on a rabbinical mitzvah and since we do perform many mitzvoth during the day without even thinking, such as helping others, doing favors, supporting our families and even listening to Torah without any specific intention at all, would it not be a good idea if at the beginning of the day a person would declare that all such unintentional good deeds should be considered as being done Leshem Mitzvah? Would that help if you latter forget?
A. Horav Shlomo Miller Shlit'a pointed out that in regards to Kavanah in Mitzvos, there is a difference between the commandments Ben Adam Lamakom, or the ones that involve only complying with the will of Hashem and the ones that additionally benefit others or society too. On the former you need intention, on the latter, it is generally accepted that after the fact you comply with the Mitzvah even if performed without intention, as the benefit was done nonetheless.
The following Poiskim maintain a similar view; Ahavas Tzion , drush 10 in the name of his father the Noda B'eyehuda, Yabia Haomer Y.D. 6: 29, also Chida in Pesach Einaim in regards to Tzedakah and Ridbaz 3: 441. However, Bais Halevy drush1, disagrees in regards to Tzdakah and Binas Simcha p. 144 compiled an extensive list of Mitzvos Ben Adam Lechavero that he considers require Kavanah.
It is also important to note that the mindful intention has to be close to the fulfillment of the Mitzvah, as Mishna Berurah (60: 7) writes: "To intent before he begins". Piskey Teshuvos (ibid. 5) mentions that the amount of time before should not be longer than the span of Hesech Hadaas, or time enough for the mind to dwell on something else. (Once you begin doing the Mitzvah with proper intention you fulfill the obligation even if you were latter Masiach Daas, see Minchas Shlomo 1:1).
Therefore a declaration of intention at the beginning of the day may not result in great benefit. However, Horav Shlomo Miller Shlit'a suggests that it may serve as a reminder to later have proper Kavanah, as we carry on with the daily Mitzvos.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit"a.