How use diaphragm properly when singing?

Slow and steady, it's best to inhale after a complete phrase so what you are singing makes sense....for example the song You're the One that I Want " You're the one that I want! *inhale quickly* You are the one for oh oh oh honey *inhale*" you wouldn't do "You're the one that I want! You are the one *inhale* for oh *inhale* oh *inhale* oh honey"

It really depends on the song. I sing chorale music most of the time. 1. When you open a song, you should always take a deep slow breath. Not only is it better for your nerves but also the way you shape the rest of the phrase. 2. Always let out all of your air between the first and second phrase , especially if there's not a lot of time to breathe in between. The more you empty your air, the faster you can fill up again. 3. Always mentally prepare your breaths before you take them, and gage how much air you will need, how quickly you will be able to take it, and where you can take it before you follow through with it. 4. Breathe deeply and fill up your lungs to their full capacity every time. Even if it's one note, it's a good habit to get into. 5. When you breathe in, your ribs should expand, or you're not doing it right. I know that this is a lot of thinking and analysis, but that's why you have practices before performances, so that you can memorize these details. Before you even begin to sing, make breath marks in the music. For example, some common ones are " ' " where you're going to take a breath and " ------------- " over top of where you're not going to breathe. Hope this helped :)