(Taken From Sefer HaMinhagim (English translation) p. 173)
1. One should endeavor to arrange that a bar-mitzvah should be called to the Reading of the Torah for his first aliyah on a Monday or Thursday morning, or at Minchah on Shabbos.
2. The blessing shepatrini (Siddur, p. 70) is said without mentioning G-d's Name. It can be said [at the Reading of the Torah] on a Monday, Thursday, or Rosh Chodesh, and not necessarily on Shabbos.
3. According to the custom of Lubavitch, people get together after Shacharis, the relatives of the bar-mitzvah say a few words in honor of the happy occasion, and the bar-mitzvah repeats a maamar of Chassidus . Those present are then offered cake and mashke, and a festive meal is held in the evening.