Ta’anit Bekhorot is moved forward to Thursday, the twelfth of Nisan (SA and Rema 470:2). As mentioned (above, 13:5), the custom nowadays is to arrange a siyum instead of fasting.
So as not to delay the start of the Seder, one should prepare the needs of the Seder on Friday: cooking the meal, preparing the ḥaroset, maror, and shank bone, and then freezing or refrigerating them. They should not be taken out of the refrigerator until after Shabbat, as it is forbidden to prepare on Shabbat for Yom Tov. Likewise, one may not set the Seder table on Shabbat. Rather, it should be set immediately upon the conclusion of Shabbat. If Seder dishes and foods were not prepared before Shabbat, they must be prepared after Shabbat.
Two sets of candles should be set up before Shabbat: one for Shabbat and one for Yom Tov, as it is forbidden to stick candles on candlesticks with melted wax on Yom Tov. If one did not prepare them in advance, he may wedge them into the candlesticks without melting them in place (Peninei Halakha: Festivals 2:2).