There are unique issues that arise when Shabuot falls on Moseh Shabbat. The Halacha prohibits "Hachana," preparing from Shabbat to the next day. Therefore, it is prohibited to make preparations for Shabuot on Shabbat. For example, it is prohibited to set the table on Shabbat afternoon for the Shabuot meal. A woman may think that she is doing a Misva by preparing early for Yom Tob. Actually, it is the opposite of a Misva. It is also forbidden on Shabbat to adjust the Sefer Torah in Shul to the Parasha to be read on Shabuot.
The question is raised whether one may sleep on Shabbat afternoon, so that he will have strength to stay up and learn all night. Hacham Ovadia permits it, as long as he doesnt verbally express that his intent is for after Shabbat.
Furthermore, one may get dressed in special Yom Tob clothing already on Shabbat afternoon, since it is also appropriate dress for Shabbat. In addition, a woman may take frozen food out of the freezer to defrost, so that it will be ready on Shabuot. It would also be permitted to go to the Mikveh on Shabbat afternoon in anticipation of the Hag.
Anything that is forbidden for a Jew to prepare on Shabbat, may not be done by a non-Jew.
It is forbidden to kindle a flame on Yom Tob. Fire must be taken from a pre-existing flame. Therefore, one should remember before Shabbat to set up a candle that will last for three days.
Finally, one should insure that he has enough "Lehem Mishneh," two whole breads for each of the seven meals that will be eaten over the course of the three day Yom Tob.
