I find its completely different holding my breath underwater than on the surface... probably because I have no choice!

I think there are three components to holding your breath well (please feel free to add more, as I don't claim to be an expert by any stretch!):

Posture: making sure your body posture is such that it maximises your lung capacity. Coming from my singing experience it will also help you if you know how your lungs work, where they start and end.

Relax: making sure you are mentally and physically relaxed which will influence posture, and consequently breathhold. This is sometimes particularly difficult in a game situation, where anxiety, anticipation and adrenalin kick in. Often nerves are the reason for poor breathhold in a game.

Familiarisation: being aware of how and when your body will react to having no air. This will most likely come through training. Being familiar with your body's reactions will reduce anxiety and stress, and most likely build confidence.

Perhaps a fourth point to consider is genetics.... some people are just closer to being a fish than others!

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