Day 52, tomorrow, will look at moving from Ushtrasana to Kapotasana. Kapotasana is an advanced position and challenging without a certain degree of preparation, key to that preparation is Ushtrasana.
The danger in kapotasana is to put too great a strain on the lower back, to avoid this we want to create a strong and stable base, ushtrasana allows us to focus on developing that stability.
Press the toes into the mat, all of them
Press the feet into the mat
Press the whole of the lower leg from the toes to the knees into the mat
Keep pressing into the mat from the moment you begin to raise your arms above your head, throughout your stay in ustrasana and until you return to vajrasana stithi
Engage your bandhas, draw up your anus and suck in the belly, imagine the muscles of the bandhas holding the base of the spine firmly, (Ramaswami's fishing rod example).
Engage the front of your thighs ( make the most of any postures that engage the quads so as to develop strength).
Most important of all bring the hips forward and keep encouraging them forward throughout all the way back into ushtrasana and throughout your stay in the posture.
With every inhalation raise up your chest and with every exhalation push your pelvis a little further forward.
As you raise your arms and lift up of your knees lift out of your pelvis and try to keep lift ion out of your pelvis throughout your stay in ustrasana.
Ideally your legs and thighs should be together, this may be something to work towards as it is less stable