These days, we are accustomed not to ask about anyone’s welfare in shul during daavening. Therefore, do not ask or answer any greetings not even between paragraphs nor during Pesukay D’zimra. (MB 2)
There is a mitzva to fear your rabbo muvhak (he is the source of your ikkar Torah) even though you are now greater than him in Torah. (MB 5)
When fulfilling the mitzva of Krias Shema (meaning within three hours), never interrupt the first possuk of Shema (including Boruch Shaym) even to answer Kaddish, Kedusha, or Borchu. (ShA 1 – MB 12)
If tefillin become available to you only after Borchu in the middle of Yotzer Or or Ahava Rabba, wait until you finish the paragraph to put them on so you can say the berachos beforehand. If they become available anytime during Krias Shema don’t say another word until you make the beracha and lay them on. (ShA 2 – MB 16)
When making the beracha on tefillin at this time say only the first beracha “lehoniach tefillin” which goes on both the shel yad and shel rosh. Omit the Boruch Shaym as well. (MB 47)
If a tallis became available to you only after Borchu you can put it on at any point except for during the first paragraph of Shema. The beracha should be recited only after Shemoneh Esray. Feel them first, then say the beracha. (Rama 2 – MB 16)
In the middle of any short beracha never interrupt even to answer Kaddish. This also applies to the sealing beracha at the end of a long beracha. (BeH “ul’kaddish”)
You should interrupt even in the middle of a possuk to answer the following responses: “Omayn. Yehay shemay rabba…” – Don’t say “yisborach”. “Omayn” after da’amiran b’alma. But not after any other part of Kaddish. “Kadosh kadosh kadosh…” “Boruch kavod hashem…” But not “Yimloch…” nor any other part of Kedusha. “Baruch Hashem ham’vorach l’olam vo’ed”. “Modim anachnu loch.” Do not continue. “Omayn” after “…hoKayl haKadosh”. “Omayn” after “…shomaya tefilla”. (ShA 3 – MB 17,20)
The above interruptions are permitted likewise during the recitation of Elokai Netzor that you say at the end of the Shemoneh Esray. (Rama 3 – MB 22)
When responding to Kaddish or Kedusha, interrupt even in the middle of a possuk – even in the middle of an inyan. Afterwards, resume daavening from the beginning of the interrupted possuk. (MB 10)
You are allowed to answer omayn to any beracha if you are holding between paragraphs. (MB 23)
If you need to go to the bathroom during Birchos Krias Shema, wash your hands afterwards but postpone the Asher Yotzar until after daavening. (MB 23)
If you are called up for an aliya while in the middle of Birchos Krias Shema you should take the aliya because of kavod haTorah. Try if you can, to finish to the end of a paragraph or at least to a verse that makes sense to pause at. Say the berachos but do not read along with the baal koray. Just listen intently. If the gabbai asks you your name you may answer him out of respect. (ShA4 – MB26)
If you are the only Cohen or Levi in shul it’s best to leave before the gabbai calls anyone. If the gabbai sees that you are in the middle of Birchos Krias Shema, he should lechatchila call a Yisroel in your stead. (MB26)
If you are the only one in shul who knows how to read the Torah, you may interrupt and read for everyone but, again, you shouldn’t be called for an aliya. (MB26)
Do not interrupt, even with silence, between the end of Krias Shema and “Emmes…” rather say “…Hashem Elokaychem Emmes.” (ShA5 – MB29)
All of the dinnim from beginning of Siman 66 until here apply as well when fulfilling the Krias Shema even without the berachos before and after. (BeH “v’ayloo”)
If you finished the Shema and waited for the chazzan, you do not need to repeat the word “Emmes…” when beginning the next beracha. (ShA6)
The poskim disagree about answering omayn after the chazzan’s “…go’al Yisroel.” Therefore avoid the machlokes by finishing that beracha in unison with the chazzan and you won’t need to answer omayn. Alternatively, begin your Shemoneh Esray (Hashem sifosai…) just before the chazzan ends “…go’al Yisroel.” – it is not apparent that you began a little earlier and is therefore still considered beginning the Shemoneh Esray together with the congregation and the chazzan. (ShA 7 – MB 35)
You must somaych ge’ula l’tefilla without even pausing. Certainly do not interrupt after saying “Boruch atto Hashem go’al Yisroel” for anything – except for laying tefillin (without a beracha). (ShA 8 – MB 46)
If you need to answer Kedusha or Borchu and you are close to beginning Shemoneh Esray, it’s best to pause before “Shira chadasha…” in order to answer to these. (ShA 9 – MB 51)
You must mention in Emmes V’yatziv the topics of Yetzias Mitzrayim, Malchus, Krias Yam Suf, and Makkos Bechoros. (MB 53)