excessive breathing leads to low levels of carbon dioxide in your blood, which causes many of the symptoms that you may feel if you hyperventilate. if you want to increase your carbon dioxide, you need to take in less oxygen.
to do this, you can breath through pursed lips (e.g. like blowing out a candle) or you can cover your mouth and one nostril, breathing through the other nostril.
breathing through a paper bag is NO LONGER RECOMMENDED because this can quickly lead to too much carbon dioxide in your blood stream