While reciting a Beracha, one should focus his attention exclusively on the Beracha, and not be involved in any other activity.
Accordingly, if a person must recite a Beracha while he drives, such as if he wishes to eat something, he should preferably pull over to the side of the road and stop to recite the Beracha. Some authorities, however, allow one to recite a Beracha while driving if it is difficult to pull over to the side. Needless to say, when doing so one should concentrate as intensely as possible on the Beracha, while paying sufficient attention to his driving so as not endanger himself.
People often begin reciting the Beracha on the Tallit as they remove the Tallit from its bag or as they shake it open. This is incorrect; all the preparations for wearing the Tallit should be completed before one begins reciting the Beracha.
Another common example of this mistake is Netilat Yadayim: many people begin drying their hands as they recite the Beracha over Netilat Yadayim. This, too, is an improper practice. One must wait until after the completion of the Beracha before he begins drying his hands. Rabbi Yosef Chayim Sonenfeld (Hungary-Jerusalem, 1849-1932) suggests a justification for the practice of drying one's hands while reciting the Beracha, on the basis of the fact that the drying is itself part of the Mitzva. Nevertheless, even he maintains that one should not begin drying until after completing the Beracha, and he made this suggestion only as a possible justification for those who follow this practice.
Similarly, it is improper to begin reciting the Beracha over a candy or other food while removing the wrapper. One should remove the wrapper, hold the food in his right hand, and then recite the Beracha.
One may not interrupt the recitation of a Beracha to gesture to somebody, such as to snap to catch someone's attention. It is very disrespectful to interrupt a Beracha one recites to God for the purpose of communicating with somebody else. The Sha'ar Ha'tziyun (notes to the Mishna Berura, commentary to the Shulchan Aruch by Rabbi Yisrael Kagan, the "Chafetz Chayim," Lithuania, 1835-1933) writes that it is permissible to snap during a Beracha only for the purpose of admonishing children in the synagogue to stop making noise. In this instance, when one snaps specifically to enhance his concentration, snapping is permissible; otherwise, it is forbidden.
Summary: One may not involve himself in even light tasks while reciting a Beracha. Therefore, one who is driving should preferably stop the car before reciting a Beracha, and the Beracha over the Tallit should be recited only after it has been removed from its bag and prepared for wearing. One should not begin drying his hands after Netilat Yadayim until he completes the Beracha. One should not begin reciting a Beracha over food until it is removed from its box or wrapper. One may not snap or make other gestures while reciting a Beracha.
