Hacham Ovadia Yosef, in his work Halichot Olam (vol. 8, p. 389 and onward), presents a number of measures that help ensure that a person remembers the Torah he studies (listen to audio recording for precise citation). First, he emphasizes the importance of studying specifically in a synagogue of Bet Midrash (study hall). The Talmud Yerushalmi establishes that a person who regularly learns Torah in a synagogue or study hall will not likely forget the material.
Secondly, Torah study should be performed "Be’sin’a," in a modest, private manner, rather than be made into a showy spectacle. The verse in the Book of Mishle (11:2) states, "Ve’et Senu’im Hochma" – "Wisdom is with the humble." Acquiring and retaining knowledge thus requires studying in a modest manner, without seeking public recognition.
Hacham Ovadia further mentions in this context the importance of studying Torah in an audible voice, rather than learning silently. This, too, helps ensure that the information will be retained and not forgotten.
Finally, Hacham Ovadia addresses the question as to the propriety of studying individually, as opposed to studying with a Habruta (partner) or as part of a group. The Gemara in Masechet Ta’anit (7) sharply condemns individual study, warning that scholars who study independently run the risk of losing their lives, Heaven forbid (listen to audio recording for precise citation). When one studies with another person or with a group, he is corrected if he learns something incorrectly, whereas during individual learning one’s mistakes go unnoticed and uncorrected. The Gemara therefore strongly demands that Torah not be studied individually.
However, Hacham Ovadia rules that this Halacha does not apply nowadays, when printed Torah literature is readily available and has become the primary means of study. Studying from a book, Hacham Ovadia claims, is functionally equivalent to studying with a study partner or a Rabbi, and therefore it is permissible to study individually from a book of Torah literature. Of course, it is always advisable to study with a partner of a group, but one who learns individually is not subject to the warning mentioned in the Gemara.
Interestingly enough, Rabbi Yaakov Emden (Germany, 1697-1776) commented that the Gemara’s warning does not apply in the Land of Israel. Since the land itself grants its inhabitants wisdom, even one who studies independently is not likely to err, and individual study in Israel is therefore permissible.
Summary: It is proper to study Torah specifically in a synagogue or study hall, in a humble, unassuming manner, and an in audible voice. Halacha discourages individual study, but studying from a book is considered tantamount to studying with a partner or from a Rabbi. Nevertheless, it is always advisable to study as part of a group or with a partner.
