Once you're able to do sets of 15-plus ab wheel rollouts from your knees, it's time to advance to the much more difficult standing variation.
Not only does a standing rollout put the points of contact (the wheel and your feet) at a further distance apart, you must also create enough stiffness through your hips and legs to hold your upper and lower leg segments together as one. Failure to do this could result in lower back injury, or at best, a failed rep.
Use these cues for standing rollout success:
As the wheel rolls further away from your feet, push down on the wheel to engage your lats. This makes the movement much more controlled. Now that your lats are turned on, they can assist in stopping the wheel and pulling it back.
As the wheel moves away from your feet, your body will begin to flatten out. Keep your abs tight and fire your quads and hip flexors to keep tension through the body. Holding an insufficient amount of muscular tension through this area will cause your hips to sag and your low back to hurt like hell.
Once you've reached the end of the range of motion, use your lats to pull the wheel back toward your feet. Properly pushing the wheel into the ground as it rolls away from you makes this task much more manageable. Failure to have done this means you now must bring the lats to tension from a less favorable position.
For each rep, strive to reach fully overhead with your arms. If you lack strength and/or mobility in the shoulders, you're likely to compensate for more range of motion by allowing your wrists to extend (knuckles going up) or by allowing your hips to sag down (placing your lower back in a vulnerable position). So keep your wrists and lumbar spine neutral. This will force the movement to take place entirely through the shoulders.
Start by mastering one single standing rollout first, then build to more and more reps.
Developing the strength to do a set of 10 solid reps will absolutely bulletproof your midsection!