This is based on my experiences and people I know. Obviously it may not always be the same for every university as they vary a lot but often the university experiences you hear about are quite similar in some aspects.
WHAT THEY DON'T TELL YOU ABOUT UNIVERSITY BEFORE YOU START
All your student loan will go on accommodation
This may depend on your student loan and how much your accommodation is, obviously, but it's likely that the majority, if not all of your student loan will be spent on your accommodation. This is mainly why I never get too hyped up over student loan payment days because I know the next day it will be going out of my bank.
You will probably only be in university up to 3 days a week
They say you will have a lot of work over the next 3/4 years, or how ever many years your course is, but the majority of that work is independent study meaning your year will most likely be 30% lectures, 70% library. I have been unlucky (or maybe lucky in a way as at least it's using the £9000 a year well) that I have had lectures everyday each year so far, maybe they'll give me a day off in my final year.
Lectures can start at after 5pm
This can be good/bad for you. Good if you like to have a lie in or focus better in the evenings, bad if you like to relax in the evenings and have dinner at a reasonable time. In my second year I had a lecture starting from 7pm and finishing and 9pm, luckily we were able to get this changed.
Halls are a 5 minute walk from university, when it's actually 30 minutes to your actual lecture building
They may be a 5 minute walk from university, but university is massive so that may be to the closest building, which is probably irrelevant to you because none of your lectures/classes are in that building. I've always had at least 20 minutes to walk to class, even when I was in halls it was 20 minutes to one of my buildings. Be prepared to walk a little further than they've told you.
Once you're behind on work, you'll forever be behind on work
The work is intense and 24/7 so you may find yourself fall behind in the semester which will then stick until that semester is over. They give you assignments every week without realising you have 1203383 other things to do already. It is extreme sometimes but you'll soon adjust to it (maybe).
The years at university go by so fast
Make the most of them. Make friends you'll have for life, jump at opportunities you probably won't get given again, step out of your comfort zone a few times...do it ALL and have the BEST time. I have had a few regrets already during my university journey so I'm going to make sure I make the most of it during my final year.