Shabbat is meant to bring holiness and rest into our lives. Making efforts on Shabbat to prepare for the week belittles its honor, and therefore the Sages forbade doing so.
Thus, one may not make the beds on Shabbat in preparation for going to sleep on Saturday night. However, one may make the beds on Shabbat so that the bedroom will look nice on Shabbat. Similarly, one may clear off a table so that one’s home will look nice on Shabbat. For the same reason, if se’uda shlishit is finished well before the end of Shabbat, one may clear the table and put the dishes in the sink. However, if se’uda shlishit finishes only a few minutes before the end of Shabbat, or if people are not planning to remain in the room where it was served, so that clearing off the table is not for Shabbat’s sake but for the week’s sake, one may not clear off the table. One who does so is expending effort on Shabbat to prepare for afterward (m. Shabbat 113a; MB 302:19).
One may wash dishes if they will be used again at some point on Shabbat. If many dishes were used, and only one cup is needed for later Shabbat use but there are no more clean cups, one may wash all the cups, since he could use any of them. Similarly, if he needs one plate but none are clean, he may wash all the plates and use one of them. However, if he does not intend to use any of them during Shabbat, he may not wash any of them (Shabbat 118a; SA 323:6; MB 323:26).
One who never leaves dirty dishes in the sink even during the week, and who feels that a pile of dirty dishes left in the sink for hours belittles the honor of Shabbat, may wash the dishes even if they will not be used again during Shabbat, so that his home will be clean in honor of Shabbat. However, even in this case, he may not wash the pots, since they are muktzeh and require burdensome work (Responsa Maharshag, OĤ 1:61; Tzitz Eliezer 14:37). (We have already seen in 13:4-5 how to clean off a table that water or juice spilled on, and in 15:9 how to clean the floor.)
One may not fold a talit so that it will be unwrinkled for next Shabbat. However, one may fold it so that it will not be left out on Shabbat in a disrespectful way (see above 13:9).
One may not prepare on Shabbat for weekdays even when a mitzva is involved. For example, one may not roll a Torah scroll to the passage that will be read during the upcoming week or the next Shabbat (MB 667:5). If necessary, one may roll the Torah scroll to the next reading and then study a few verses from it, so that the rolling will serve a purpose on Shabbat as well (AHS 667:2). One may bring a book to the synagogue if it is needed after Shabbat, as long as one studies a bit from it on Shabbat as well.
On Shabbat one may study for a test in a Torah subject that is scheduled for the upcoming week, since studying these topics is itself a mitzva. However, it is proper not to study on Shabbat for tests in secular subjects. First, Shabbat must be dedicated to Torah study. Second, the student’s primary goal in studying is to succeed on his test, not to become more knowledgeable. In a time of need one may be lenient, since there is intrinsic value to secular studies. In contrast, one may not study a foreign language on Shabbat, because such study has no intrinsic value. It is also prohibited to study for a test in a subject that normally involves writing exercises, because (as we saw) one may read on Shabbat only when there is no concern that one might end up writing or erasing.
One should not say on Shabbat, “I will go to sleep now, so that I will have energy after Shabbat.” This belittles Shabbat, since he is using it to prepare for weekdays. However, if he does not verbalize this but only thinks it, it is not forbidden, since sleeping on Shabbat is a pleasure (Sefer Ĥasidim; MB 290:4; see above 5:3).
When Yom Tov follows Shabbat, one may not prepare on Shabbat for Yom Tov. Be-di’avad, if one prepared something on Shabbat for afterward, he may benefit from his actions.