Build strength by not focusing on straight Army style situps, but half downs, half ups, full range, and other abdominal exercises. I harp them but I never found an exercise that was more demonic than the buddy leg throws for abs. Couple that with extended depression by being over a ledge with your legs, ass right on the edge (basically gripping the edge with your hands, under your ass) so you get an extended range of motion.
Then, for Army situps, your back's gonna get sore if you crunch too much. Keep your elbows apart and use your upper arms as propulsion. Throw your elbows wide on the return from vertical, and use them to help you get momentum from flat on your back. Exhale for more "space" to crunch on the way up, inhale on the way down. That'll help you do more.
Don't start the heavy crunches and basically going to "shitty form" so to speak, until you NEED to "cheat" to get that last 10 or 5 reps.. then you spool up the meter. Just like you do the first 10 perfect, then after you do 10 you start milking to what the "minimum acceptable" is for your grader, since the fact is regardless of what the manual says, graders have different eyeballs and see things differently.
Don't yank on your nugget either, try to keep as little tension on your head as possible. Yanking on your melon isn't going to help you do any more and if you are going chin to chest... well, you're a medic, I was a medic of sorts, there's a ton of medics, EMT's, Paragods, PJ's and even a couple sorta-cool-guy Doctors here... what's chin to chest? What do we rectify doing ABC's and what do we do for positioning of the head on a casualty? Don't occlude your own airway willingly, even if you are a maladjusted Kiwi who likes the wrong side of the street in Thailand.
The other thing is for prep/training/whatever, try to rock out with a good closed cell pad and/or on terrain that isn't shittastic. OSUT at benning we were doing our PT tests on an asphalt parade field with a 1/4 mile track around the outside of it. Wonderful, eh?
