1) Learn to touch type.
2) Keep a diary/journal. If you want to become an MG or YA writer, to have access to a seven- or ten- or fifteen-year-old's thoughts will be invaluable. (Plus the whole process of getting used to writing regularly.)
3) Do your best at school. Learn everything you can.
4) Take an interest in lots of different things. You don't have to pursue them right to the end of whatever course they take, but it will give you a broad range of topics to write about later.
5) Try new things for the experience.
6) Read a lot. Read a lot. Read a lot.
7) Find another career to support yourself until your writing takes off.
8) Save and back-up your files regularly, and email drafts to yourself.
9) The first draft can be rubbish. THAT IS OKAY!! The subsequent drafts are where the story takes shape and the magic happens.
10) Get your butt in the chair and WRITE.
11) Persist. Don't give up.
12) Keep a notebook with you (& especially on your bedside table) to jot down ideas while you remember them. Write down the date, too.
Anybody have any other tips?