You need to rest it after throwing, if you don't do this it will get hurt. Your muscles will tear if you dont, let it heal, and that will cause injury.
Step 1: Helping Your Arm Heal
You will need to ice it to reduce swelling, if it gets swollen that can prevent you from throwing for awhile. Swelling leads to injuries because it tightens everything in the arm.
Step 2: Keeping Your Arm in Shape
You will need to stretch your arm daily, you will notice that after throwing it will be much harder to because your muscles will be tight. That is why it is important to stretch it. Resistance bands will strengthen the smaller muscles in your arm, making them have more endurance when throwing. Running is also important because increase in leg strength puts less stress on the arm when throwing, and core work outs also.
Step 3: The End
That is all you need to know to keep your arm healthy.