We found that Adho Mukha Svanasana was one of the steadiest poses (though not easy!) to try. Key points were to start with a wider stance then usually and to maintain a strong contact with the center of your palms on the board. Engaging our legs more than usual also seemed to steady out the pose. Have fun! 
Wheel pose (Chakrasana) was a bit more challenging but surprisingly steady once in the pose. Be sure to stay calm and relaxed in your breathing before pressing up, lift your heart to the sky and press strongly into the board with your hands and feet. (warm up the spine with a few cat/cows prior to coming into this deep back bend). Hope you give it a go!
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