When you inject into a new muscle, I would always start with very small shots. I would opt for about 1/2cc per shot at first. Then add more as the site gets used to it. If I have an injection start to hurt, i take advil right away and often use heat instead of ice, The heat helps to loosen the muscle up and bring in fresh blood to carry the waste away. As for needle depth, it's going to depend on body fat. If you are heavier, you might want to use a 1.5in pin, but if you are lean, a 1in should be enough.
Make sure that you give a good rest to every injection site. I won't inject into a site any more than 1x wk