Here are some suggestions that I would recommend on your pre-arrival and first two weeks of settling down:
Before you arrive in Hong Kong, if your arrival date is earlier than the student residence check-in date or the check-in date of the apartment you rent, make sure you have booked somewhere else in Hong Kong that is comfortable to stay. In my case, I booked a hotel in Sha Tin for two nights before going to check in at the CityU's student residence.
Have some spare Hong Kong dollars and coins ready before you arrive, so it will help you get through the first few days of your arrival by covering your expenses on public transportation and food, water, and other necessities. I recommend several hundred to one thousand Hong Kong dollars and coins on top of the U.S. dollars you will bring to Hong Kong.
You should obtain an Octopus card at the MTR station as early as possible. Go to the in-person kiosk at the station entrance and let the worker know you want to obtain an Octopus card and deposit an X amount of cash into that card. The maximum you can deposit into the card is HKD$3000. There is also an Octopus App that you can download from the App Store to keep track of your balances and spending. You may refill your card balance at the station's in-person kiosk, ticket machines, and authorized convenience stores.
If you are going to study in Hong Kong for a year, you must apply for a Hong Kong ID card, and the first step is to schedule an in-person appointment online. The available appointment spots tend to fill up at an inexplicably fast speed, so you must make an appointment as soon as possible after you arrive in Hong Kong. This does not apply to exchange students staying in Hong Kong for only one semester.
In the Festival Walk shopping mall, students tend to go to Taste, a supermarket, to purchase water, towels, tissue paper, bread, etc. There is also a crowded food court on the uppermost floor where you can order from hotpot, Japanese-styled food, Cantonese-styled food, and Kentucky Fried Chicken. On the opposite end of the food court lies Uniqlo and a few souvenir stores if you are a fan of new clothes, toys, mini-figures, etc. Other than these places, people often visit the Apple store, movie theater, bakery, and bookstore that is also situated around the center region on the same floor of the shopping mall.
When passing through the airport customs, the officials will give you a small slip of paper - a legal permit to stay in Hong Kong. If you lose it, you will have many unnecessary problems if you were to leave Hong Kong temporarily during the semester and return to Hong Kong to finish your studies.
Last, do not forget to purchase a three-pronged type-D or type-G power adaptor as Hong Kong, a former colony of Great Britain, still applies the former British electricity standards. Then, ensure the type-D or type-G power adaptor you own is compatible with your power cords to charge your devices successfully. Another variation would be to purchase a three-pronged type-D or type-G adaptor connected to a power strip where you can plug in multiple, various types of adaptors and power cords simultaneously.