Reasons to love this pose for SUPing : It's FUN and it feels great to open this twist up and trust that as you drop your gaze back, you'll keep floating.
Modifications : Stay low on the back knee to mellow the balance aspect.
Personal notes : I love sweeping the top arm forward and back, over head and all around. This flowing arm movement feels great in the shoulders and creates a bit of momentum to lift the hips.
Start in a low lunge.
Set up your alignment, right knee above the right ankle. Left leg stretched out long behind you. Heel-toe the right foot away from center so that your base is opening up. Pick up the right toes and pivot them out towards the right rail of your board. Take a couple breaths before moving on.
With both hands on the board, tuck the left toes under and press up, off of the left knee. Now the left leg is engaged and energized.
With an inhale, start to pick the right hand up and reach it towards the sky. Maintain awareness of the left toes, left hand, and right foot. These are the contact points that keep your balance so trying to distribute your weight evenly will be important.
My favorite variation is to pivot on to the outer edge of the left foot. This change of footing ups the challenge but allows you to open the twist more. Think Side Plank in that left foot. Press actively through the left heel and use the motion of pressing down (at your contact points) to lift the hips up. Check in with the right toes repeatedly. Keep them active to support the right knee.
Once you've established your base, explore some movement through the (top) arm. Reach up and maybe back, opening the chest towards the sky. Reach towards the tail of your board then arc the arm overhead towards the nose, building a strong lifting sensation (my personal favorite). Or simply find stillness.
When you're ready, roll back out of the twist to your low lunge and into downward facing dog or take a Vinyasa to reset for the other side.