I learnt this from Smitty of Diesel Crew so if you get a chance make sure you check out his stuff.
In the core training exercises that follow our goal is to remain as neutral as possible. That is a neutral spine and pelvis so that a straight line could be drawn from top of the head, through the upper back and down to the sacrum. This neutral spine position is also maintained for exercises like the straight leg sit up and the Romanian Dead Lift. Our goal with all our core training is to resist rotation and extension by engaging all of our core musculature (our stabilizers as it were) and to create enough tension through the system to get stronger. It’s all about time under tension and movement quality. We must also develop good respiratory control so we are able to breathe over the brace, especially where tension is at its peak which will allow us to own the movement. Respiratory control is particularly important as it will transfer into our sport and other daily activities. It is this same control we must bring back to all activities that we perform because losing it has ramifications up and down the kinetic chain; loss of joint centration, loss of pelvic alignment, upper/lower cross syndromes and the ability to obtain neutral posture at rest or under loads.
As seen in the video above Supermans are done by setting up in a push up position. From there you walk your feet back as far as you can and then reverse the movement so you come back up into the start position of the push up. It is important that while you keep your entire body braced in a neutral position you keep breathing even when tension is at its peak. You may also want to think about engaging your posterior chain i.e. turning on your glutes, spinal erectors and lats. The most important consideration is quality of movement. Sure we want more time under tension to get stronger but not at the expense movement quality.