First, wrap the comic book in bubble wrap to provide cushioning. Then, place it in a sturdy cardboard box and fill any empty spaces with packing peanuts to prevent movement during transit.
You should pack a comic book for shipping like this: Get a box that's just the right size. Put the comic in a protective bag or sleeve, and then place it in the box. Add some bubble wrap or other padding materials to make sure it doesn't move around. Seal the box well and label it clearly.