As and when you feel fatigue or distractions or when you need to increase concentration, you can practice deep breath with full inhalation and slow exhalation initially for 5 times. Later on, you can slow it down to 6-10 deep slow breaths in a minute. Practice for 5 minutes will suffice. This would help you refresh and increase focus.
Deep breathing can be better practiced if it is abdominal breathing. In abdominal breathing, your abdomen inflates as you inhale and your abdomen is contracted inside towards your spine as you exhale. You must have seen such breathing in a new born baby. This breathing slowly reverses to thoracic (chest) breathing as we grow. Such abdominal breathing also helps you to destress yourself. Few practices every day will help you adopt such breathing at normal rate.
In nutshell, the general target points are abdominal breathing and slow exhalation.
You can also practice Naada - Anusandhana Pranayama.
