It is easier to be at mental peace when you are in meditative places. The challenge is to keep your inner peace when living a modern city life that may be too demanding. The inner peace is at your hand when the breath flows through sushumna.
There are many yogic practices that force the prana through sushumna. One of the famous mudras is 'Maha mudra' which is a set of hatha yoga poses. This mudra is said to have the power over death. Such is the power of that mudra and it is usually taught under proper supervision in Kriya yoga lineages. If done properly, it prepares the body for the activation of sushumna. Naturally, the prana starts moving through sushumna if one is into a system of meditation that works directly at the subtler levels.
The breath naturally shifts between the left and right nostrils and flows through sushumna for a brief moment. Our goal is to get it flowing through sushumna, most of the times. I would like to introduce a simple technique which would work readily for many. It is possible to shift the flow of breath with the mind itself. The best way to keep the breath flowing through sushumna is to keep the focus/awareness on the bridge between the nostrils. In the picture, I have shaded that region red. The statue seems not to have hole for the nostrils.. Never mind! :) Good luck on the path of self mastery!