Dwi pada pitam: Two-foot support is very similar to bridge pose (setu bandha or setu bandha sarvangasana), although the emphasis is less on opening the chest/arching the upper back, and more on maintaining a straight line of energy from shoulders to knees. Sinking the weight into the heels, the hips float up light as a feather.
Dandasana: The foundation for seated poses, staff pose requires effort and concentration to ensure the whole body is actively engaged – legs, arms, abdominal and spinal muscles – plus (if working with the energy locks) all three principle bandhas can be involved, too.
Drishti: The practice of drishtana, directing the gaze, is integral to Ashtanga yoga and is very useful in balancing poses like the one shown on the left (natarajasana). Our proprioception relies heavily on visual cues and it takes practice to be able to move the gaze (or even close the eyes) while balancing. Sometimes, as in the image on the right, drishti is a meditative tool; directing the gaze towards the third eye affects ajna chakra and can help still the mind.
Dharana: This is one of Patañjali’s eight limbs of yoga and translates as concentration. We need to focus our thoughts on a single point or object of contemplation, directing all our energy towards that point alone, in order to discipline the mind and begin the process of meditation. From there we can move on to dhyana, where energy flows in both directions, before reaching samadhi, where subject and object merge (or rather, we realise that duality is an illusion). Drishtana is a form of dharana, one might say. See here for a reference to dharana in the Mahabharata (in Spanish) and a short essay (in English) based on the same reference here.
Embrace yoga 