Learn the proper freediving breathing techniques. Slowing your heart rate down and minimizing your oxygen consumption is called the breath up. Learn how to get good gas exchange in this video with Erin Magee.
Erin Magee teaches you how to prepare before your dive using the breath up. Focus on good gas exchange and stay relaxed. Focus more on the diaphragm rather than your shoulders and upper respiratory muscles. The more you can move your breathing down lower the better; this is diaphragm breathing. Start by breathing in and out through your diaphragm without your upper chest moving.
Next, take a short pause and when you exhale do a nice relaxed exhale. Try this out by breathing in through your teeth, restricting your flow, pause then slowly let it out with a slow exhalation through pursing your lips.
The slow exhalation breaths are going to slow down your heart rate for a few minutes before your dive. Don’t forget to keep the pauses in your breathing pattern, lowering your heart rate and oxygen consumption. Practicing this will really increase your breath hold and your bottom times on your dive.