20:7 When the shaliach tzibbur finishes the repetition of Shemoneh Esrei, he should quietly say the verse “y’hiyu l’ratzon imrei fi” but he does not take three steps back, relying on the steps he took after his personal Shemoneh Esrei. (If he does take the three steps, it’s not a problem – Mishnah Brurah 123:19.)

20:8 On a public fast day, when there are ten people present who are fasting, the shaliach tzibbur says “Aneinu.” (Mishnah Brurah 566:14 acknowledges a practice to say “Aneinu” if seven are fasting and the rest are only eating because they must for health reasons.) Aneinu is recited at shacharis and mincha. It should be said before the blessing “Refa’einu.” If the shaliach tzibbur forgot but remembered before saying God's Name in the conclusion of the blessing, he goes back and says both Aneinu and Refa’einu. If he has already said God’s Name, he must complete the blessing of Refa’einu and insert Aneinu in the blessing of Shomei’ah Tefilla, like an individual does. If he forgot it there, too, he says it after the Shemoneh Esrei without a blessing conclusion. (Mishnah Brurah 566:13 says that if there are not ten fasting, the shaliach tzibbur says Aneinu in Shomei’ah Tefilla, like an individual.)