Accept your offer! They won't wait around for you forever, so make sure you know the deadline. Every university is different, but all have a phone number you can call or a help page on their website if you have any difficulties or enquiries.
Do not buy your 'recommended' textbooks yet. Often your lecturer or tutor will tell you which ones you will need (if any).
Plan your timetable. All universities have a master timetable you can access for all subjects. If you plan it in advance and jump online as soon as class enrolment is open, the chance of you having to endure a 9am on Friday - or any day - is significantly less.
Lost on Campus panda! (Google images)
If you own a smartphone, the Lost on Campus app could save you. Download it, it's free. It will tell you where you are, where your building is, or even the nearest toilet. Rather than being the awkward Jaffy asking everyone for directions, be the kid who walks around glued to their phone.
It would be a long, lonely experience if you don't have many friends at uni; join some clubs and societies to meet people. There's plenty to cater for every interest, or if you've always wanted to try something but never had the guts, go for it. It is unlikely that you will ever again have thousands of people your age this open to new friendships so you might as well take advantage of it.
Talk to a career or core advisor if you can. Assuming you know what you want to do with your future career, they will ensure you are on the right track. If you are absolutely clueless, they can help you choose subjects that will keep your options open for as long as possible.
Find free calendars in magazines - this one's from Frankie
Get a calendar and write everything on it: test dates, assignment due dates, breaks and SWOT Vac (you don't want to be that kid that comes to class on Easter Monday). Often a lecturer will go over this in your first class, and it helps to have it all somewhere you can see easily. It will keep things in perspective, and stop you from turning up to that 9am exam at 9am the day after (it happens).
Prioritise. Yes, you want to have a fantastic time with your new mates, but if you have a mid-semester test the next morning you should probably go home. There's no bell-curve here - if you fail, you fail. Same goes for spending: buying lunch every day is easy, but at a minimum of $50 a week you'll be left wondering why you can't afford that booze cruise.
Finally, have fun! This is the only time in your life you have the irresponsible excuse of youth and the legal freedom of an adult.