We've done both these topics before, but they are particularly appropriate for Yom Kippur.
V'AL KULAM, E'LOHA SLICHOT, S'LACH LANU, M'CHAL LANU,
And what do many, many people do in this powerful, dramatic moment with this powerful sentence? They mispronounce G-d's name. They say ELOHA. That's not correct. The last syllable is not -HA.
Just as apple isn't TAPUCHA, and altar is not MIZBEICHA. Why not? Because the CHET with a PATACH at the end of a word is pronounced PATACH first and then the CHET. This is the "PATACH GENUVA" (stolen PATACH) rule of Hebrew pronunciation.
The rule not only applies to CHET, but to HEI and AYIN as well. Less obvious and often missed, but PATACH GENUVA applies to all three letters.
Practice saying AHHH, the interjection that expresses satisfaction and pleasure, rather than HA, the interjection that expresses triumph. AHHH, the bath water is at a perfect temperature. Not HA, I won the game. The last syllable of the name of HaShem in the above sentence is AHHH. The PATACH sound first, then an aspirated HEI. AHH.
The ALEF with a CHATAF SEGOL does not really consitute a syllable of its own, but is attached to the LAMED-CHOLOM - ELO, with the accent of the word being on the LO part of the ELO syllable.
eLO-ahh. That's the Ashkenazi way to pronounce this name of G-d. S'faradim don't pronounce the PATACH GENUVA as if it were under an ALEF, but rather a VAV (pronounced like a W) or YUD, depending upon the preceding vowel. eLO-wahh. Apple is ta-PU-wach (Ashkenazim would say ta-PU-ach). Altar is miz-BEI-yach.
The point: The two "proper" ways to pronounce ALEF-LAMED-VAV-HEI are eLO-ahhh or eLO- wahh. Not eLO-ha. Lots of people have been saying ELOHA for so long that they will resist this correction. It takes practice to say it right, but it is G-d's name and we are asking Him for forgiveness. It's worth the effort.
The other issue is the AMEIN CHATUFA, the premature AMEIN. Many chazanim and baalei t'fila invite an AMEIN before they finish the last word of a bracha, by stretching the last word(s). This is especially so on Yom Tov. HaMelech HaKaaaaa- aaaaaaaaaaaaaa-dosh. As a result of habit or the chior-style response, it is extremely tempting to say AMEIN while the chazan stretches the last word. Halacha trumps habit and choir-style put together. The halacha is clear that we must not answer AMEIN until the one saying the bracha finishes it completely. (And then, we must be careful not to delay it, creating an AMEIN YETOMA, an orphan AMEIN. Also halachically forbidden.)
It is just too ironic to be davening on Yom Kippur, when we are supposed to be doing as good a job of davening as possible, and mispronounce G-d's name or improperly answer AMEIN. Obviously, there are many other things we should be extra careful about on Yom Kippur. This was just two. Okay, here's another one. In one's zeal to daven (the silent Amida, for example) with extra kavana, one sometimes raises his voice loud enough to disturb others. This too is ironic: Trying to daven at the cost of committing an interpersonal sin that requires further, difficult, T'shuva. G'MAR CHATIMA TOVA