Do you mean how to get deeper into meditation through breathing? Or how to just take larger breaths? If the former, how deep are you already?
Step one: Inhale. Step two: Inhale deeper. No, this is not sarcasm. You should also look into three part and five part Yogic breathing. For three part, focus on your belly, then fill your lower chest, then upper chest. For five part, fill your lower abs, your upper abs, your lower chest, upper chest and your sinuses. It takes some focus to be able to do this correctly, but you will breath deeper as a result.
Let your attention rest on the flow of your breath. Listen to it, follow it, but make no judgments on it (such as "It sounds a little raspy...maybe I'm getting a cold?"). The goal is to allow the "chattering" in your mind to gradually fade away. Find an "anchor" to settle your mind.
