I have added crunches to my workouts most days. If I do them at the gym, I used the piece of equipment that is my featured photo. This secures your feet above you, so no chance of slipping off of it, and all you do is raise your body, breathing out, and making that crunch at the top. I hold it for 5 seconds, and then come back down.
If I do them at home, I put a couple of cushions on the floor for my head, lay flat, and bring my body forward as much as I can possible get it. I breathe in when laying down through my nose, and breathe out when sitting up, and going forward as far as I can. Then breathe in as I lay down.
I am also doing lots of squats, as these type of exercises don’t put any pressure on my shoulder, and I want to get back to tight abs again.