So update from me, one week and a bit in.
Am REALLY glad to doing a challenge that is NOT daily! And is something I can work in with my normal routine. Don't think I could do a daily challenge every month.
So far I been working predominantly planks in between sets 3x a week. My trainer went through some form tips to really hit the abs (and he'd sit there digging a finger into my mid regions to make sure everything was tight...).
Need to activate and squeeze your glutes and try to roll the front of your hips in/up as far as you can. Shoulders were right back and down, and the middle of the chest out. This makes your glutes to your shoulders as "flat" as can be on the back.
Foot/toes were in as far as they could be to take strain away from the legs. And the plank wasn't completely straight from top to bottom - it was completely level/parallel to the ground from hips to head, with the legs needing a little angle.
Most videos I've seen make you fully straight and the toes point straight down. I played around a bit and definitely felt it more with the changes I described above.
Also completed this on Saturday as well, and will try to do weekly:
About cx30
30 minutes of sideplanks, wood chops, assorted crunches, resistance band movements etc.
I have also sorts of sore bits around my abs and on top of my lower ribs even. Progress I guess!