Although modern day concept of yoga is synonymous to phyical postures or stretching, yoga is actully about mind and contemplation.
Give yourself a few minutes of contemplation every day. Think of all the positive things happened that day. Also think of negative things and see if you can turn them into positive experience by letting go of your anger and ego. Apply the balm of love on the unpleasant situation and see if this helps turn the events from negative to positive in your own mind. This few-minute-a-day regimen of contemplation will help you improve your health. Your mind becomes calmer, any ailments will slowly reduce their severity, your sleep improves and you feel healthier and happier. It takes consistent and persistent practice to feel the difference. That is how we purify our self.
According to Patanjali, this is called Swadhyaya and is one of the Niaymas which a yogi is to follow before taking up yoga postures.