Study a single sutra by selecting the pada (chapter) and then the sutra (verse).
Source: English translation from The Yoga Sutras of Patanjali (Sri Swami Satchidananda)
When disturbed by negative thoughts, opposite [positive] ones should be thought of. THis is pratipaksha bhavana.
Source: How to Know God: The Yoga Aphorisms of Patanjali (Swami Prabhavananda, Christopher Isherwood)
To be free from thoughts that distract one from yoga, thoughts of an opposite kind must be cultivated.
Source: English translation of the Yoga Sutras of Patanjali (Swami Jnaneshvara Bharati)
When these codes of self-regulation or restraint (yamas) and observances or practices of self-training (niyamas) are inhibited from being practiced due to perverse, unwholesome, troublesome, or deviant thoughts, principles in the opposite direction, or contrary thought should be cultivated.