Manually breathing, it’s the only time I ever really get a full breath. If you consciously breathe, you’re forcing your body to take deeper breaths.

Making sure I’m hydrated. I’ve noticed that when I get dehydrated I feel like I’m not breathing as deeply. Also taking one puff on my inhaler and then waiting 10-15 min before taking my 2nd.

In addition to what everyone is saying, if you just need a quick deep breath, you can hold your arms up with your hands resting on your head, and it can feel like it "frees up space" to allow for a deeper breath. Additionally, if you are concerned about your actual oxygen saturation, a pulse oximeter can be helpful. I hope that you are able to find something that helps!