Maintain solid spinal alignment. Most people who are new to this will want to cheat the single-arm plank by creating cervical hyper-extension and tilting their heads up. This strains the neck and places excessive tension on the lumbar spine by causing the hips to sag.
Focus on keeping a tall and elongated neck throughout rather than tilting the head up or down.
This exercise teaches you to hold the shoulder girdle rigid to avoid strength leaks in pressing lifts. It strengthens the front delts, rotator cuff, and even the lats.