Reviewing the prayers:
The Chazan for Rosh Hashanah and Yom Kippur should review the Davening, the meaning of its words, and the Midrashic and Chassidic teachings on the prayers. This especially applies to the Piyutim in Davening. This is to be done every year even if he did so the previous year. He is also to review the laws of prayer in general and especially those that specifically pertain to the Chazan. Every individual is to review the prayers and teach it to his children prior to the Holiday.
The Piyutim: Whoever has the ability is to take out time to learn the meaning of the Piyutim recited during the prayer.
Correct punctuation and Nussach:
During the ten days of repentance, which begin from Rosh Hashanah, one must be extra careful in punctuating the words of Davening correctly. Due to this a number of laws regarding punctuation and dialect of wording is recorded in Poskim.
 Beir Heiytiv 581/7 “Learn the prayers and supplications”; Igros Kodesh 6/324; 11/353 and 416 [brought in Shaarei Halacha Uminhag 1/247; Shulchan Menachem 3/93]; See Mateh Efraim 581/48; 585/2; Darkei Chaim Veshalom 702; M”A 581/9 in name of Shlah “Learn the Kavanos”
 Igros Kodesh ibid; Shaareiy Teshuvah 584/3
 Rebbe ibid
 Igros Kodesh 11/353
 Kaf Hachaim 582/26; Mateh Efraim 581/58
 Shaareiy Teshuvah 584/3; Kaf Hachaim 584/13
 The reason: Since these are days of judgment [the words one says, even if his intent is otherwise, have affect, thus] one is to place special care in pronouncing the words with their correct punctuation. However during the rest of the year we do not suspect for a mispronunciation as [G-d] follows the person’s intention behind the word. [ibid]
 List of words and their correct punctuation, and correct Nussach: Lechaim versus Lachaim [Admur 582/7]; Lechaim Tovim versus Lechaim [582/8]; Mentioning Rosh Chodesh; Yom Teruah versus Zichron Teruah [582/9]; Omitting Moadim Lesimcha; Omitting Vehasieinu; Omitting Ein Anu Yecholim in Musaf [582/10] Udvarcha Emes versus Udvarcha Malkeinu by both Haftorah and Kiddush [582/11; Siddur-Udvarcha Malekinu Emes; Shaar Hakolel 42/11; Poskim in Kaf Hachaim 582/55] Shehashultan with Kamatz versus Shehashilton with Chirik [582/12; Levush; Taz 582/2; Mateh Moshe; Peri Chadash brought in Kaf Hachaim 582/37] Veharisha with Chirik under Shin. [582/13] Vechein Tzaddikim versus Az Tzaddikim [582/14] Yom Teruah Mikra Kodesh and Zichron Teruah Mikra Kodesh versus Beahava Mikra Kodesh. [582/14; Poskim in Kaf Hachaim 582/41] Uvichein Yiskadesh Shimcha-four times Uvichein based on Kabala. [Kaf Hachaim 582/35] Hayom Haras Olam-according to Kabala. [Kaf Hachaim 582/36] Aguda Echas versus Eguda Echas with a Patach or Segol [Mahril; Kneses Hagedola; Peri Chadash; Kaf Hachaim 582/37] Vesikva Tovah Ledorshecha versus Vesikva Tovah [Kaf Hachaim ibid in name of Arizal] Kol Harisha versus Ki Kol Harisha [Mateh Moshe 796; Kaf Hachaim ibid] Beashan Tichleh versus Keashan Tichleh [Mahril; Mateh Moshe; Peri Chadash; Siddur Rashash; Siddur Admur [Beashan]; Shaar Hakolel 42/6; Likkutei Mahrich 63a; M”E 692/14; Darkei Chaim Veshalom 711; Kaf Hachaim 582/37] Saying Beyom Menuchaseinu on Rosh Hashanah that falls on Shabbos [Poskim brought in Kaf Hachaim 582/48] Meloch Al Kol Haolam Kulo versus Meloch Al Haolam Kulo [Poskim brought in Kaf Hachaim 582/50]
Lechaim versus Lachaim Tovim: First one is to mention Lechaim and only afterwards in Ukesov Lechaim should he say Lechaim Tovim as first one asks for a small requests and then increases in asking for more. [582/8]