Decide what qualification or electronics engineering discipline you want to do after you leave as it will dictate what you should take over the next few years. I highly recommend asking your current science teacher or faculty head who the most experienced teacher in electronics in the school is and seek them out for advice. See if they have any extracurricular jobs at school related to electronics and see if you can get into that teachers class, just ask them!
Math, Physics, Programming and hands on like Robotics, Design and Workshop are used in electronics. If you have spare subjects take anything technology related.