If you are still at school, and you have a good idea that you would like to be a journalist when you leave in the future, you will doubtless be looking to organise your life such that it supports your choice of career. Indeed, you will find that there are steps you can take towards your goal even at this early stage.
To start with, you need to focus on practising and developing your language skills and style so that these are well-suited to the business of journalistic writing. If you can, join your school's newspaper, or start one of these if it doesn't already exist; all experience, from investigations into the safe use of raticide in your local supermarket, to writing up reviews of the amateur dramatics society's latest product, is equally as important and useful.
In addition to beginning your journalistic career as early on as possible, you will also want to ensure that you find a university that offers courses that suit your specific purpose. Start to do research into this area as early on as you can; this way, you will have plenty of time to prepare a portfolio of work should the application require that you submit one.
In addition, you will want to try to tailor any work experience opportunities offered to you by your school so that these help you to further your goal. If you can, secure places at your local newspaper; this experience will doubtless prove immensely useful in the long run.
If you are keen to take on a career as a journalist, you would do well to begin working on this as early as possible. Try to get as much exposure to the profession and experience as you can; this will help you to hone the right skills from the outset.