Picture 2+3 lower the leg from the hip, try to keep both legs, the one lowering and the one remaining straight by stretching through the whole leg right up to the toes.
Engage mula bandha by drawing up your anus and then uddiyana bandha by drawing your belly back and up at the end of the exhale, this hollowing of the belly will allow you to lower the last inch or two to the floor with control.
Raise the leg back up to standing slowly with control on a long inhalation, there's a tendency to take the leg back up quickly, thinking that the important aspect of the posture is the lowering of the leg.
Both the lowering and raising of the leg are vinyasas.
Between picture 3 and 4 we can include an extra vinyasa in which we bend the knee to bring the right foot into the left groin then bend the left knee to bring the knee towards the forehead. This can act as a preparatory vinyasa for Supta ardha badha halasana.
It's also possible to include yet another vinyasa where we bring the right foot to the left goring then lower the left leg bringing the toes to the floor above our head. This is an unbound version of Supta ardha badha halasana
It may be advisable to work on the bind in the On one leg sequence or asymmetric where one foot is in half lotus and the is a more stable base.
In Sarvangasana, bing the right foot to the left groin and lower the left leg slightly. Support the back firmly with the right arm, making the right leg good and straight by engaging it strongly.
Use the left hand to bring the right foot deeper into the left groin. Return the left hand to support the back and then swing the right arm around the back twisting the hips to gain better access to the right toes.
It's may be useful to think of the action of putting on a jacket in which the second sleeve has become a little tangled.
before lowering the foot to the mat, try to straighten up and relax the shoulders as much as possible
Gain a firm hold of the right toe with the right hand and lower the left foot to the mat above your head..
In Halasana, Picture 6, lower both legs to the mat above your head first then stretch the arms to the floor
Engage bandhas, enabling you to draw in your belly to create the space for a deep fold.
Inhalation will be shorter than normal but exhalation can be long and slow, stay for 6-12 breaths.
For urdhwa-mukha-paschimottanasana, picture 8, take the the toes as in picture 7 and work towards a deeper foold as in paschimottanasana in the seated sequence over a number of breaths. For the first three hold the toes, the next three fold deeper and take the side of the feet, with the next three breaths take the heels if that feels available to you.
This is an extreme forward bend and you will want to make sure that your hamstrings have been sufficiently warmed up and loosened earlier in your practice.
NB: These are practice notes that will be tidied up and put into the new edition of my Vinyasa Yoga Practice Book along with the current sequences and subroutines. The book can be freely downloaded HERE. There is a page on Facebook HERE with all the latest sheets and updates. This book is in no way a substitute for Ramaswami's Complete Book of Vinyasa Yoga.