The process depends on what are you going to study and for which degree (Undergraduate programs/ Graduate programs/ Doctoral degrees/ Post-doctoral fellowships, various internship programs). For exact instructions and deadlines, please advise your future department/ supervisor.
The academic year in Israel usually starts during October (academic year 2020-2021 will start October 18, 2020).
BA/B.Sc./M.Sc., PhD students should arrive before the academic year starts. Besides the courses you might take at your first semester, there are a few issues to take care of, such as finding suitable accommodations (dorms/ an apartment on the private market, roommates search, etc.).
Post-Doctoral fellows should arrive accordingly to an agreement with their supervisor, but please note that it is easier to find suitable accommodations before the start of the academic year (or of a new semester).
For your convenience and easier decision making, here are the dates of the major Jewish holidays for 2020. Most of the Israeli governmental offices, BGU included, in Israel and abroad, are closed through the holidays, and some – even more. It means that the procedures as visas, health insurances, etc. – are to be taken care of in advance.
Purim – March 9-10
Passover – April 9-15
Independence Day – April 29 (it is a national holiday, the private businesses and the transportation work, the governmental office don't work)
Shavuot (Feast of Weeks) – May 28-30
Rosh ha-Shanah (Jewish New Year) – September 18-20
Yom Kippur (Day of Atonement) – September 27-28
Sukkot (Feast of Tabernacles) – October 2-9.
The weekend in Israel is during Friday and Saturday.
When you know the date of your arrival to Israel, the most important issues to take care of before arriving are: registration to BGU, visa and health insurance.