Translation:Shulchan Aruch/Orach Chaim/251
251: Not to Perform Work on the Eve of Shabbat from the Afternoon and Onward. Contains 2 Seifim.
1 One who performs work on Erev Shabbos from the Minchah and onward does not see a sign of blessing. Some explain: Minchah Gedolah; and some explain: Minchah Ketanah.
Gloss: And specifically purposefully setting about to perform significant work. However, if one performs them in a casual way for an hour and it is not significant it is permitted. (Beis Yosef in the name of Or Zarua). And therefore, it is permitted to write a casual letter and anything similar (his own words).
2
To fix one's clothing and vessels for the need of Shabbat is permitted during the whole day.
Gloss: And the same law applies to his friend's clothes, if it is for the need of Shabbat and he does not receive payment for it. Beis Yosef.
And the same law applies to one who writes books for himself in the course of his study.
Gloss: But it is forbidden to write for his friend for money (Mordechai, Chapter "A Place where they are Accustomed"). And one may get a haircut all day even from a Jewish barber (Kol Bo and Beis Yosef). And a person should lessen the amount he studies a little on Erev Shabbat in order to perform the necessities for Shabbat (Shilte Giborim, Chapter 16 of Shabbat; Yerushalmi, first chapter of Ta'anit).