Translation:Shulchan Aruch/Orach Chaim/251
1. Not to Perform Work on Friday from the Afternoon Onward, 2 Seifim: One who performs work on Erev Shabbos from Minchah time and onward will not see a sign of blessing. Some Mefarshim say Minchah means from Minchah Gedolah and some Mefarshim say it means Minchah Ketanah. RAMA: Specifically purposefully setting about to perform significant work. However if someone performs a casual task for an hour and it is not significant it is permitted. (Beis Yosef in the name of א"ז). And therefore, it is permitted to write a casual letter and similar.
2. It is permitted to fix one's clothing or vessels during the whole day. RAMA: This is the law as it relates to his friend's clothes, if it is necessary for Shabbat and he does not receive a reward (Beis Yosef).This law applies to one who writes books for himself in the course of his studies. RAMA: But it is forbidden to write for his friend for money (Mordechai). One may get a haircut all day even from a Jewish barber (Kol Bo and Beis Yosef). There are those who lessen the amount they study on Erev Shabbat in order to perform all the necessities for Shabbat.