We have four main breathing techniques for meditation. Natural, Reverse, Prenatal and Tortoise. A brief explanation will suffice here. Natural breath is when we breathe in and the lower abdomen expands like a balloon and contracts upon exhalation. Reverse breath is when we breathe in and the lower abdomen contracts while upon exhalation it expands.
Prenatal breath is when the lower abdomen and upper abdomen do reciprocal movements.
Tortoise breath is the same only the breath is held in for some time before exhaling to allow the outer and inner Qi's to mix. It is important not to try the last three breathing techniques too soon, at least three years should pass on each technique before going on to the next. The tongue is always pressed lightly to the upper palate just above the tooth line for all of the meditation techniques. The chin is pulled in lightly but not forced. If saliva forms, swallow it and breathe out to 'send the golden elixir' to the tan tien, an electrical point about three inches below the navel.