Something I've been paying attention to lately is leg raises, very much work in progress.
It's something I have difficulty with, just can't seem to get my leg straight. It's been getting a little better though, every time I'm in Shoulderstand I tend to lower my right foot/toe, say, to the floor near my head and then allow the left foot to drop back to the floor behind me which takes the right foot straight up, then I bring the left foot back up and repeat on the other side. think this is called dakshina pada uttanamayurasana rightside peacock stretch pose
There are also leg raises in some of the Shoulder stand prep, the dwipadapitam vinyasa, (table posture).
If you can do it in Shoulderstand then why not headstand. This isn't in Ramaswami's book The complete book of Vinyasa krama but as the Italians say, it marries. I was pleased with this, I've never dropped back in headstand before, although we came close to trying it on the course. My first time trying it is caught on the video below. It's always scared me a little as I use the wall so have never fallen out of headstand. You have no idea how far away the floor is but I've got into this from the ground up so figured my body knows what it's doing. What do we think dakshina pada viparita dandasana?
And if Table pose, shoulderstand and headstand then why not Urdhwa dhanurasana (wheel pose) I drop back ten times a day, might as well practice them here too. Again not in the book but I saw a video of Tony Sanchez doing it and it was such a classic pose that I've been wanting to try it. He has his leg completely straight, see it here about seven minutes in. Notice he drops back by raising his heels. I don't tend to do this ( I splay my feet instead) and a lot of teachers it seems will get on your case about it and give you some anatomical reason why it's a bad idea but, Mr Sanchez has been doing this for a while and it looks elegant, kind of En pointe.
Because I was recording I've rushed things a little below, generally in Vinyasa Krama you would raise the leg on the inhale, lower on the exhale and repeat three to six times, or perhaps on the third go you might hold the leg up there for three breaths gently nudging the tailbone up higher at the end of each exhalation and again lower on the exhale.