When I get impatient with myself I look at my old pictures. In 2011 I had to hold my foot that is behind the head. I had not yet found out how to keep it behind the head without holding it. The trick: The leg must be engaged. It's even easier if the toes are pointed and when the leg moves in this direction.
All of my forward bending asanas improved because I get a perfect adjustment in paschimottanasana after urdhva dhanurasana from M every day when I practice in the shala. I want to add that I didn't exercise eka pada sirsasana for about 2 years. I started exercising it again since one month. Nevertheless it improved a lot.
I wanted to write about something else: How to learn?
I think one must study the asanas. If one doesn't question the own practice it can be that one is stuck for decades. When a pose doesn't improve after let's say 3 years something goes wrong!
Examples: Practicing handstand against the wall leads to nothing but frustration. It's the wrong method to learn it.
Another example: I used to take a strap around my legs when I practiced laghu vajrasana. My ability to come up from this pose faded away that way. My legs got weaker. Instead of keeping the legs parallel with my own strength, they drifted apart, but the strap prevented this. To come up didn't happen either.
One can use props, but one must really know how to use it. Before using props one must have understood the pose.