First of all you have to see whether you have enough percentage/ CGPA that your school requires you for the two streams. If you qualify for both and are confused then decide what you like doing most. Choose subjects accordingly. Science subjects would include at least three out of Physics, Chemistry, Biology and Maths. Arts subjects would include wide number of options like History, Geography, Political Science, etc. So, based on your choice of subjects you can choose the stream. Moreover, decide your subjects and stream based on your career choice. So, make your choice accordingly.

All the best!