When Yom Tov begins as Shabbat departs on Saturday night, we must take care not to prepare on Shabbat for Yom Tov. Shabbat is meant to be holy and restful, not a day to prepare for another day. Making efforts on Shabbat in order to prepare for a weekday or Yom Tov is an affront to its honor (see Peninei Halakha: Shabbat 22:15-16).
Therefore, washing dirty dishes on Shabbat in order to use them on Yom Tov is forbidden. Only after Shabbat may they be washed for Yom Tov use. It is also prohibited to clean the table on Shabbat to honor Yom Tov; however, it is permitted to clean it so that it looks nice on Shabbat, even though it will also be helpful to have the table clean for Yom Tov.
Le–khatḥila, on Shabbat that will lead into Yom Tov, one should have se’uda shlishit relatively early – more than three hours before the end of the day. If he did not manage to do so, he should still have se’uda shlishit, even if it is close to Yom Tov. However, he should eat minimally, so that he has an appetite for the Yom Tov meal (Rema 529:1; MB ad loc. 8).
One who leaves for synagogue while it is still Shabbat may take a maḥzor with him. He should look at its contents a bit on Shabbat, so that his taking it will have served a purpose on Shabbat.
Contemporary poskim disagree about whether one may remove food from a freezer on Shabbat to be used for a Yom Tov meal. As a practical matter, under extenuating circumstances, such as if waiting until after Shabbat will cause anguish and a considerable delay to the beginning of the Yom Tov meal, food may be removed on Shabbat. However, absent such necessity, one should be stringent and not remove food from a freezer on Shabbat for use on Yom Tov (see Ḥarḥavot).
When Shavu’ot follows Shabbat, it is better not to announce that one’s nap on Shabbat is in preparation for staying up all Shavu’ot night learning Torah. Nevertheless, one who wishes to say so may, since the main prohibition is to speak on Shabbat about something which is prohibited on Shabbat, and Torah study is not prohibited on Shabbat. Furthermore, such a statement does not take away from the honor of Shabbat, since it is for the sake of a mitzva.
When Yom Tov begins on Saturday night, the Yom Tov candles may not be lit until after tzeit. One waits until Shabbat is over, recites “Barukh ha-mavdil bein kodesh le-kodesh” (“Blessed is the One Who distinguishes between the sacred and the sacred”), and then lights (section 2 above).
Since it is prohibited to light a new fire on Yom Tov (below 5:1), it is necessary to light a candle before Shabbat which will last for more than 24 hours, and from which one can light the Yom Tov candles. If one forgot to do so, he should go to neighbors and “borrow” a flame from them in order to light the Yom Tov candles.
In Ma’ariv that night, we do not recite Ata Ḥonantanu, which speaks about separating between the sacred and mundane. Rather, we recite Va-todi’enu, which speaks about separating between the greater sanctity of Shabbat and the lesser sanctity of Yom Tov. One who forgot to recite Va-todi’enu does not repeat the Amida, because he will make havdala later over a cup of wine (SA 491:2; MB ad loc. 4). If he wants to do melakha relating to food preparation before havdala, he should say “Barukh ha-mavdil bein kodesh le-kodesh.” This law also applies to women if they do not pray Ma’ariv but would like to do melakha before hearing havdala (MB 299:36).
In the Yom Tov kiddush recited that night, we add a havdala section, including the line “ha-mavdil bein kodesh le-kodesh” (“Who distinguishes sacred from sacred”). We also recite the berakha over fire, “borei me’orei ha-esh” (“Creator of firelight”). However, no fragrance is used, because normally, fragrance is meant to soothe the soul’s pain at the departure of Shabbat. When Yom Tov follows Shabbat, there is no pain, so there is no need for fragrance to soothe it.
The order of kiddush is as follows: the berakha over the wine; the berakha of kiddush over the sanctity of the day; the berakha over fire; the berakha of havdala; and She-heḥeyanu (SA 473:1). The Gemara’s acronym to remember this order is “yaknehaz,” which stands for yayin (wine), kiddush, ner (candle), havdala, and zeman (She-heḥeyanu).