[jimmux]

The most effective technique I have used is also the simplest. I came across it reading about how trauma affects the body. Under stress we tend to exhale more forcefully in short outward breaths, so when exhalation is quicker than inhalation the body responds accordingly. This means we can get a beneficial response if exhalation is longer than inhalation.

So the technique is to inhale at whatever pace feels comfortable, counting if that helps, and then exhale a little longer. It soon becomes natural enough that no counting is necessary and you can think about whatever pleasant associations work.