Adding Velocity and strengthening my arm

I am a junior in high school and I was wondering if anybody could give me any tips on how to add speed to my pitches as well as strengthen my arm–make it last longer…

well the best wayof strengthening your arm is lots of long toss nd weight lifting, ut also, whether you can change your mechanics i dont know

without good mechanics good luck lasting one inning let alone 9. work on them first