Improving your breathing begins with learning about what you are already doing.
3 times every day, (morning, afternoon, evening) stop for at least 3 breaths and notice how your breathing feels. Your breath enhancement practice will develop as a result of your observations. Begin to figure out what the one thing is that you need to practice. Are you:
rushing
gripping your gut
clenching your jaw
You are the boss of yourself. Your breathing will listen if you tell it what to do!