Hey Doc7. I'm about to finish my first year of the IB. What I would suggest is definitely know what courses you will be taking. If there is any summer homework for your classes, obviously do that. Also if I could go back in time, I would have done some research on the requirements of the classes for the courses I am in now, that way I would not have been so confused and overwhelmed by the workload.
But you have already downloaded this app which is more than what I did at your age, so I'm sure you'll be fine.
Have fun et bonne chance! Salut!!!