To develop sthira in an asana means to have the ability to hold the body in a posture with strength and steadiness for an extended period of time. This skill can be developed through the whole body with regular practice of yoga, strengthening the muscles so that they can be engaged without tension. It also means needing the breath to be even, smooth and rhythmic in order to allow the posture to be held without strain.
There are other aspects of a yogic lifestyle which can help increase sthira in yoga and in daily life. For example, eating a healthy diet with meals at regular intervals cultivates sthira in the body.
Sthira can also be cultivated in all relationships, by practicing patience, steadiness and equanimity in interactions with others. The initial yoga practice of developing sthira will also promote patience within one's self. This patience enhances stability, which has a positive impact on relationships.