The first limb consists of the yamas, or universal ethical observances. The second of the five yamas is satya, or truthfulness. Like building blocks, each yama rests upon the foundation that the ones before it create. Satya follows ahimsa (non-violence), the first and most important of the yamas. Hence we cannot practice truthfulness without first considering the principle of non-harming. In telling the truth we should aim to cause the least harm possible. If speaking the truth will cause pain or suffering, then it may be best to remain silent.
So the practice of satya is not about blindly and heedlessly telling the truth regardless of consequences. It is much more about restraint: about taking our time and carefully considering our thoughts and words so that the way in which we express the truth is in harmony with ahimsa. Yoga is first and foremost a practice of awareness. Practicing satya in accordance with ahimsa requires awareness of the effect our words and thoughts have on others and ourselves.
We may bring this practice of satya onto our mats by always assessing ourselves honestly. We look at all parts of each pose that we assume, the parts that flatter us and the not-so-flattering parts. We practice the asanas we shine in as well as those that humble us. We face our strengths and our weaknesses with the same curiosity and kindness. We always work at our own level and honor where our bodies are each day.