Interlace hands behind head.
Stay here or lift feet up in line with face (more doable: bend knees until big toes touch floor).
Squeeze legs together, tighten glutes, firm hamstrings, tone abdomen.
Minimize rounding in low back.
Lift chest, stretch spine.
Extend legs out.
Soften face, eyes. Breathe as evenly as possible.
Like boat, in half boat, low back must float. You must lift your chest, stretch your spine, start to finish. For the sake of your low back, do not allow any part of your spine to collapse. I almost always say in class, “Half boat, twice as hard as boat.”