The most widely used technique in the UK is called active cycle of breathing techniques (ACBT). It involves repeating a cycle made up of a number of different steps. 

These include a period of normal breathing, followed by deep breaths to loosen the mucus and force it up, then coughing the mucus out. The cycle is then repeated for 20 to 30 minutes. 

Do not attempt ACBT if you have not first been taught the steps by a suitably trained physiotherapist, as performing the techniques incorrectly could damage your lungs. 

If you're otherwise in good health, you'll probably only need to perform ACBT once or twice a day. If you develop a lung infection, you may need to perform ACBT on a more frequent basis.