Sit in a comfortable position of yoga with your spine straight, close your eyes, enhale deeply and hold your breath as you also lower your chin towards your chest (your chin tries to touch your chest). When it will be for you difficult to hold your breath any longer exhale slowly.
With this method you can learn to control the volume of air inside your lungs so check the time as you inhale.
If you cannot hold your breath for more that one minute then the volume of air you keep in your lungs is not suficient. If you can hold your breath one minute and half your cardiovascular system works pretty well. if you can keep your breath 2 minutes or more you have a Yogi's breathing capacities!
Alexander - Northern Deer