How can I help my teenager prepare for uni?

Firstly, it is important to assist your son develop goals that are realistic and achievable. For example, if science is not his strength - then a career in medicine may not be the best choice! Often school's have career advisors that assist him in this area.
Secondly, it's a big ask for anyone in their teen years to “decide” what they want to do as their career…..so perhaps take some pressure off him by allowing him to think about what he enjoys and what he is good at, and remove the whole “career” pressure. 
Finally, structure is important as well as balance. Help him structure his time, while at the same time allowing him time to spend with friends etc… 
With regard to studying specifically, he will need to develop skills to prioritise and break tasks down into smaller parts. A study timetable may work, however I find many young young people find these more stressful. Instead, help him manage his anxiety by being supportive and encouraging regular breaks while at the same time helping him problem solve where applicable.

I agree with Leanne. In addition I would suggest that you find a buddy for him - someone already at uni who could show him around, act as a mentor and encourage him. If you don't know of anyone you can contact University Counselling Services and they can assist you in finding a mentor.

Learning how to learn is not something schools often teach. We can often presume children should just know how to study and attain knowledge without actually taking them through it specifically. The whole idea of learning about learning and thinking about thinking comes under the heading of metacognition.

I was one of those students at school  who didn't know how to study. it wasn't until I left school and a few years after that, I discovered the knack of how to learn. As a consequence I ended up duxing my undergraduate year as a mature age student (early 20's) and then after a few teaching degrees and psychology degrees later I realised I had actually got the hang of it. What clinched it for me was a very real and authentic interest in the topic of study.

University study is a means to an end… the goal being a job or career that is of interest.

I can remember when I was choosing a PhD thesis to research talking with potential PhD supervisors across a number of different universities around Australia at the time… I was offered a position researching a particular topic that I new I could do but it wasn't really in my area of interest. I can remember asking… If I had a choice of a research topic that was already prepared for me to jump in to or something else that I was more passionate about what would be the best thing to choose? Every supervisor said to me; if you are going to dedicate such a large chunk of your life to it, you had better be passionate about it and interested in it… or else you won't make it through.

So I chose a research topic and related university offering the topic that interested me and what I was passionate about.

PhD's are the highest level of academic achievement and so in this context it is generally recognised that to study at a high level you need to have an intrinsic motivation for the topic being studied, a real interest and genuine enthusiasm for the line of work that it involves and a commitment to learning what ever is required to fully understand the area of focus.

University for university sake can actually be a big time waster. Students of anything, whether a degree, trade or anything else need to be genuinely interested in what they are learning or else they really will not have the motivation or interest to learn it.

So it's about your child finding their passion and interest. What sparks their interest and builds a sense of purpose and/or invigoration thinking about the possibility of developing the skills and building the knowledge in it? 

it can be quite an exciting time as the teenager starts considering possibilities for their life. What they want to do and the things they want to dedicate their time to learning over their late teenage/early adult years.

Feel free to email if you would like to talk a little more on this.