After Shabbos is over, and having said “Baruch hamavdil bein kodesh lekodesh” (or davening Maariv), light Yom Tov candles.
When bentching licht, the berachos of Lehadlik Ner Shel Yom Tov and Shehecheyanu are said.
Maariv
Say the Shemoneh Esrei for Shalosh Regalim, adding the paragraph of Vatodi’einu.
This is followed by the complete Hallel. Hallel is followed by Kaddish Shalem and Aleinu.
The Seder
Begin the Seder as soon as possible, so the children will not fall asleep.
The Rebbe Rashab once told the Frierdiker Rebbe: “During the Seder, and especially when the door is opened, we must think about being a mentch, and Hashem will help. Don’t ask for gashmiyus; ask for ruchniyus.” (The Rebbe’s Haggadah)
“The Haggadah should be said loudly, with great joy and much kavanah.” (Siddur HaArizal, cited in Likkutei Sichos vol. 22, p. 179 fn. 40)