One way singers can maximize the air in their lungs is to "open" the sides of the body for better inhalation. For now, think of your ribs and your sides as separate. The sides are the love handle area — the area right below your rib cage and above your hips — the oblique muscles. This area may automatically open when you open the ribs, but you want to be sure.
Place your hands on your hips and then move them up a couple of inches so that you feel the indentation just above the top of the hipbone.
Pretend that your lungs are on your sides and inhale, to help open that area. You may also be able to open this area by placing your hands on your sides, exhaling, and then opening your hands. You may need to provide a little resistance with your hands so you can figure out how to open those muscles.
Your sides are a great place to notice exertion in the body. When you cough, you may feel your abs move in and your sides expand. The movement for singing is similar but happens more slowly. The sides also engage when you sing loudly. For now, be aware of how your sides move; later, you can move your sides when you need an exertion of energy to sing loudly.
Singing with a clear tone doesn’t use as much air as singing with a breathy tone. You can sing with a breathy tone on purpose, but it requires a lot more air and it’s more difficult for a microphone to amplify a fuzzy tone.