On the first day of Pesach, we recite before Musaf the special "Tikun Tal" service, marking the transition to the new season in which we recite "Morid Ha'tal" in place of "Mashiv Ha'ru'ach" in the Amida. We begin reciting "Morid Ha'tal" during Musaf on the first day of Pesach. Somebody who mistakenly recited "Mashiv Ha'ru'ach" instead of "Morid Ha'tal," and realized his mistake only after concluding the Beracha of "Mechayei Ha'meitim," must return to the beginning of the Amida.
If somebody is uncertain whether he recited "Morid Ha'tal" or "Mashiv Ha'ru'ach," then during the first month after the first day of Pesach he must assume that he recited "Mashiv Ha'ru'ach," and must therefore repeat the Amida. One can avoid this situation by reciting on the first day of Pesach the passage "Mechayei Meitim Ata Rav Le'hoshi'a Morid Ha'tal" ninety times, thereby training his tongue to recite "Morid Ha'tal." One who trains his tongue in this fashion may then assume that he recited the proper text and will thus not be required to repeat the Amida if he cannot remember which text he recited.
Preferably, one who wishes to employ this technique should repeat this passage a hundred and one times, rather than just ninety. The Gemara in Masechet Chagiga (9) comments that studying material one hundred and one times ensures that it will not be forgotten, and thus here, too, reciting the correct text of the Amida a hundred and one times helps guarantee that one will recite the Amida properly. Furthermore, since familiarity is obtained after a month of reciting the new text, it is preferable to recite it one hundred and one times to include not only the ninety daily Amida recitations, but also the recitations of Musaf on Shabbat and Rosh Chodesh.
Throughout the festival of Pesach, including Chol Ha'mo'ed, one adds "Ya'aleh Ve'yavo" in Shacharit, Mincha and Arvit. One who forgot to add this paragraph and realizes his mistake only after concluding the Amida must repeat the entire Amida.
Hallel is recited throughout the festival of Pesach. However, after the first two days of Pesach (or after the first day in Israel), Hallel is recited "Be'dilug" – meaning, omitting the sections that are omitted on Rosh Chodesh – and without a Beracha.
Musaf is recited on each of day of Chol Ha'mo'ed; however, when reciting Musaf on Chol Ha'mo'ed – as opposed to Yom Tov – the words "Yom Tov" are omitted from the phrase, "Yom Tov Mikra Kodesh Ha'zeh." Nevertheless, one who mistakenly recited "Yom Tov Mikra Kodesh Ha'zeh" on Chol Ha'mo'ed is not required to repeat the Amida.
The second day of Pesach, or the 16th of Nissan, is the day on which Haman was killed during the Purim story. It is therefore proper to make some commemoration of this event during one's meal on this day, a practice often referred to as "Se'udat Ester." At this meal one should speak words of Torah relevant to Ester and the Purim story, to commemorate the Jews' miraculous salvation that took place on the 16th of Nissan.
(Based on Chacham Ovadia Yosef's rulings in Chazon Ovadia – Laws of Pesach, p. 247-249)
