Shulchan Aruch – The Halachot of Rosh Hashanah
Note: The RAMA is in brackets [ ]
Chapter 582: The prayers said on the עשׂרת ימי תשׁובה (ten days of attonement) and Rosh Hashana.
1. On the עשׂרת ימי תשׁובה we say המלך הקדשׁ (the holly king) and המשׁפט המלך (the holly judge) . If one erred or is in doupt if he said it: If it was המלך הקדשׁ, you must return to the beginning. If it is המשׁפט המלך, then if you remember before moving your feet (3 steps backward by “he who makes peace ...”) then you go back to the beginning of המלך המשׁפט and say it there, and then continue with the normal order. But if you didn’t remember until you move your feet, then you must repeat the Shemona Esray from the beginning.
3. On the Shabbat between them, at מעריב (the evening service) you say המלך הקדושׁ like the rest of the impending week. [And if Rosh Hashanna fell out on Shabbis, you say the blessings of the impending week at מעריב and the same applies if Yom Kippur was on Shabbis.]
4. There are those who have the custom to pray on Rosh Hashana and Yom Kippur bent over. However, they must straiten out at the end of the blessings.
5. If one did not say זכרנו (“remember us for life ...”) and מי כמוך (“who is like you, father of compassion...”), he need not repeat them [even if you finished the blessing but didn’t move your feet yet. The same applies if one didn’t say וכתוב and בספר.]
6. On Rosh Hashanna, we say “ותתן לנו את יום הזכרון הזה” (“and he gave us this day of rememberence”) and we don’t menchan Rosh Chodesh (M.B: Even if Rosh Chodesh falls out on Rosh Hashana, we don’t menchan it in the prayer since it is also called יום הזכרון).
7. If Rosh Hashanna fell out on a weekday, you say “יום תרועה מקרא קודשׁ” and if it fell out on the Shabbat, you say “זכרון תרועה”.
8. We don’t say “מועדים לשׂמחה חגים זמנים לשׂשׂון” and “והשׂיאנו”. In מוסף (the additional service) we don’t say “ואין אנו יכולין לעלות ולראות לפניך” but we say instead “ואין אנו יכולים לעשׂות חובותינו לפניך” [and end wih “... ודברך אמת” ].
9. Even though the rest of the year we pray quietly, on Rosh Hashanna and Yom Kippur the custom is to pray loudly. We are not worried that others will (be disterbed by the noise) and err (in praying) since they have the means to go back (and start the prayer over). [It is customary that everyone tells his fellow “לשׁנה טובה תכתב” (“you should be inscribed for a good year”).
Translated by Jay Dinovitser www.shulchanarach.com
 This is in place of “holly G-d” (הקל הקדשׁ ) and “the king who loves righteousness and judgment” we normally say in the Shemona Esray prayer.
 תוך כדי דיבור is the time it takes to say three words like “good morning teacher”.
 M.B. says that this only applies if he did not start this next blessing. If he started the next blessing after saying הקל הקדש , then evenׁ תוך כדי דיבור would not help and he must repeat the Shemona Esray prayer.