Who thought that you could do something as natural as breathing wrong? It's true!
Most people take frequent, shallow breaths, which actually requires more effort than deep breathing. Shallow breathing also triggers a mild fight-or-flight response, and sensitive Fish don't need that kind of grief!
Do double duty by practicing deep breathing while you do yoga or lift weights.
It's common to hold your breath when you concentrate, but if you exhale with the effort (lifting a barbell, doing an ab crunch), you'll make your breath work for you, activating your core and stabilizing your spine so you can do that Sun Salutation more efficiently!