Holding your breath doesn't mean what you think it means. Your epiglottis, the flap that switches your throat from esophagus to trachea is stronger than your lungs. Meaning if you hold your breath, which for most people means closing your epiglottis, it can cause a lung overexpansion injury if you ascent over too large of a pressure gradient. I.e. take a full breath on scuba to where you can't fit any more air in, hold it in with your epiglottis closed and ascent from about 7-10 feet, your lungs will explode *literally explode, your lungs can't take much pressure, which is why there are a whole lot of dangers about positive pressure regulators and no breathing victims, which if you ever take an O2 delivery course for CPR/First Aid etc, they will explain all of that* and you will die, game over.
Don't do that. That doesn't mean you have to have a constant inhale exhale, just means don't close your throat. If you are sitting down, start to exhale and then stop the exhale, most people will raise the back of their tongue a bit, and it will feel like the beginning of a cough, which means your epiglottis is closed. Now, inhale, and stop inhaling, if you move a little bit air will either come in or go out naturally with your bodies motion, your epiglottis is open and life is good. This is the feeling you want to maintain on scuba.
For mask exhalations, you inhale normally, tip your head back, crack the bottom of the mask ever so slightly and exhale quite slowly from your nose. If you do it with any sort of force it will just blow the water around and not purge it, this is why you don't want to open the bottom of the mask too much, bad news bears. Think of a hose with pressure trying to fill a bucket, splashes around everywhere, but if the hose is turned down in pressure, then it just fills the bucket nice and easy.
With our students we make them watch the water lever in their mask go down quite slowly, takes lots of practice to learn to do right. The other fun exhalation drill is making them with masks off exhale so slowly that one bubble comes out of one nostril, then the next bubble comes out of the other one and it goes back and forth. Disclaimer to that, university class, so we have a lot more time to make them good at skills like that.
Disclaimer: no actual medical advice given, but really, don't hold your breath