Is yawning permitted during Shemoneh Esrei?

It is forbidden to yawn or belch during Shemoneh Esrei. If a person feels compelled to yawn, he must cover his mouth and stop reciting the words for the duration of the yawn. A person who burps involuntarily is not culpable for transgressing this halacha. He does not need to cover his mouth in this case, since it does not open as wide--or for as long--as it does when he yawns.

סצ"ז ס"א ס"ק א' ביאורים ומוספים דרשו 1

Is spitting permitted during Shemoneh Esrei?

Spitting is forbidden during Shemoneh Esrei. If one feels the need to remove saliva that gathers in his mouth, he should expel it into a garment in such a way that the saliva will not be visible. If it is customary in the region for people to wear a bib-like garment, some Achronim allow a person to spit into the bib even if saliva is visible. Others do not make this distinction. If a person is finicky and will not spit into a garment, he should turn his head and spit backward. If this is not an option, he should spit to his left. Spitting to the right, forward, or upward is forbidden, since it appears as if one is spitting in the direction of the Shechinah. If it is impossible to spit to the left or backwards and a person is under duress, he may spit forward or to his right.

ס"ב ס"ק ה'-ח'

Should a tallis be adjusted during Shemoneh Esrei?

If a person’s tallis partially slips off during Shemoneh Esrei, he may adjust it back into place. If it slips off entirely, putting it back on is forbidden. Picking it up is considered a hefsek. Another person may put it back on for him.  If he did pick it up, he does not have to start the brocha over again. After Shemoneh Esrei, he should touch the tzitzis and recite a brocha. Other Achronim disagree and hold that a new brocha is not necessary. In earlier times, it was common for glasses to slip off the face. One who is concerned that his glasses could fall off during the bowing in Shemoneh Esrei must fasten them in place.  

ס"ד ס"ק י"ג-ט"ז ביאורים ומוספים דרשו 13, 14

• During Pesukei D’zimrah, Kriyas Shema or Shemoneh Esrei, one may not hold an object which he would want to prevent from falling to the ground. The focus on holding the item would disturb his concentration on davening. Examples of objects which are forbidden to hold include tefillin, sifrei kodesh, knives, money, a loaf of bread, keys and walking sticks.

• If a sefer falls in the middle of Shemoneh Esrei and the fallen sefer is disturbing one’s kavanah, picking up the sefer is permissible at the end of a brocha.  It is forbidden to motion or point to get others to pick up the sefer.

• A person who wants to daven from a siddur should make sure that the siddur is available before he starts Shemoneh Esrei. If he will be saying any additional sections, these passages should be prepared before davening; he should not be leafing through the pages during Shemoneh Esrei.

• How should one mentally prepare for Shemoneh Esrei?

• At what age should children be brought to shul?

• What is the proper perspective for tefilla?