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.
Do a split squat, then only come about three-fourths of the way up. Hold that position for 3 seconds before lowering. Great for the glute medius and minimus.