( In the email I was asked for suggestions about coming. The sender wrote that they've been able to dropback for a long time but still can't make it back up. This is pretty much my response but with some of the video's embeded rather than linked too. It's a very personal response relating what's worked for me).
Like you, I dropped back before learning to come up, isn't it supposed to be the other way around? I seem to remember being given a hard time on the blog because I was doing 2nd series without having come up first.
I remember I first came up almost by surprise, there's a video on the blog where I kind of cheer a little, that was the first time. Ahhh, here it is, I still cringe with embarrassment watching it, oh well....
I've included a lot of video's in this post. If you watch them in Youtube there's a link in the Yotube comment to a post where I discuss the point of the video a little more.
No doubt, like you, I was working on the rocking back and forth, walking in on Urdhava danurasana, trying to throw the hips forward, that kind of thing.
I think there's a trick to it, getting the timing right. I don't think you have to be super strong and flexible (although a little of both), just a case of getting the hip/pelvis action right, there's a shifting it forward but there also seems to be a lifting up through the pelvis too.
I think it helps to work on dropping back to something like a couch/futon and just work on noticing what's happening in the hips, finding the point where it 'bites' as you come up. Try and fix that motion in muscle memory and then start dropping a little lower and then lower still, all the time noticing and fixing in your mind and body the action so you can try and 'catch' that same point coming up.
I still tend to drop back close to the wall. I don't need to, I can drop back and come up without but I like to take some of the pressure off of the first couple and not strain. So I'll walk out from the wall three steps, work into it a little then drop back. I'll start to come up but will generally tap off the wall, even sometimes walk my hands up the wall a little to come up that first time. kind of easing into it. I have that luxury practicing at home, harder in a shala I guess
I tend to keep dropping back and coming up until I get three really nice one's in a row.
Just before you drop back, try and lift up out of your pelvis, lengthening your body, keeping your legs as straight as possible as you start to take it back. Don't let yourself drop right away but keep bending back and stretching up through the hips and pelvis, pushing them forward. You'll probably find that at some point this pushing the hips forward will throw your body forward without meaning too kind of like a spring, play with that it will carry you back up the last of the way.
When you do try to come up, try and think about straightening the legs, lifting up through the hips rather than just pushing them forward. Use the wall, you might not get up all the way and may need to push up off the wall at first but it's a start.
It's so difficult to describe, there are several elements all happening at once, one of them will be the missing piece that will take you up.
The breath helps, I used to really snatch at the breath and find that half way up my lungs were full and it would kind of stop me coming up any further. Inhaling more slowly as you come up is tricky but it means that the breath helps to take you all the way up. Maybe it's not the breath but the leading with the chest but it feels like the breath.
As for my feet I've switched to lifting my heels slightly as I drop back and come up but when I come up at the end of practice from urdhva danhurasana I still turn my feet out. Not good technique perhaps. Your teacher might be making you keep your feet parallel. It's harder that way but if you can learn it then it'll look prettier. Harder to improve technique later if you get into bad habits.
I don't know if any of this will help you, perhaps there'll be something that might make the difference.
Sorry this is all a bit chaotic but I wanted to send some suggestions off straight away.
To sum up my main suggestions.
1. Practice dropping back to a couch or futon and coming up from there to fix the action your aiming at in your mind.
2. Practice at the wall, pushing or tapping off to come all the way up
3. Try to straighten the legs as much as possible, even while in Urdhva Danhurasana
4. As well as pushing the hips/pelvis/groin/tops of your thighs forward, try and get a lifting motion as well as forward. THE LIFT BACK UP HAPPENS FROM THE HIPS/PELVIS (for me anyway).
5. Try to inhale all the way up, don't fill your lungs too quickly.
Hope something here helps, good luck with it. I'm sure it'll happen completely by surprise one day.
That will be a good day.
I'll try and turn this into a blog post then perhaps, in the comments, readers will give tips that worked for them.
Oh one more thing. My suggestions above are from practicing at home, no couch/futon in the shala. If you want to do some extra practice at home then perhaps a little stretching to warm up. This is a Vinyasa Krama ten minute routine that has some nice back stretches ( I start all of my practices with this, even Ashtanga).
Then perhaps a couple of Urdhava Danurasana on the mat and finally work on easing into dropping back at the wall, something like this.