Article in English: It is highly advisable that you practice holding your breath with a partner. The main reason for this is that they can ensure your safety if you happen to pass out (which is fairly common during limit-testing training sessions), preventing you from hurting yourself and taking care of you while you recover your senses. In addition, a partner can help to time your breath-holding sessions, notifying you at each 30 second interval. The best position to practice holding your breath in is sitting upright in a comfortable position, such as on a sofa or armchair. This allows you to expend as little energy as possible while holding your breath. It is not advised that you lie down while holding your breath, as you run the risk of choking on your tongue if you happen to pass out. Although the purpose of learning to hold your breath for longer is usually for use underwater, you should never do underwater training alone, without supervision. As mentioned before, it is quite common for people to black out or lose consciousness after holding their breath for prolonged periods, and if this happens underwater it can lead to drowning.  Even practicing with a partner can be dangerous, as an untrained eye may be unable to tell the difference between someone who is holding their breath and someone who has passed out.

Summary in Vietnamese:
Luôn luôn luyện tập với một người cộng sự. Luyện tập bằng cách ngồi thẳng, thay vì nằm. Đừng cố gắng thực hiện việc này dưới nước trừ khi bạn được giám sát bởi một chuyên gia.