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.
A training program doesn't have to be complicated to work. In fact, sometimes the most simplistic routines can be the most exhaustive and result-producing.
Erick Minor's got a bone to pick: he keeps encountering personal trainers who make assertions about training athletes that just don't pan out in real life conditions, i.e. the gym and the athletic field.