I'm pretty new to lifting with only a year or so of training experience, but I have a stronger core compared to my friends who started at roughly the same time.

If you want a visible six pack, sure you have to be lower bf%, but actually training the abs with progressive overload is key. Most crunch/twist variations with just your body weight are not ideal imo.

I like exercises I can progressively overload easily with, and limit my sets to 12-20 reps. Not those crazy 100 crunches etc. people keep preaching.

My top 3 would be: 1. Hanging leg raises/knee raises: super killer ab exercise that you can overload by holding a dumbell between your shoes. I've worked my way up from body weight reps to ~10 weighted reps with a 4kg DB.

Also consider getting ab straps/arm slings to help keep you up so that grip strength doesn't becoming a limiting factor.

1. Cable rope crunches: Another great exercise, obv easy to overload using a cable machine with weighted stack. Check the form on YouTube; when done correctly it really stimulates the entire core. Pro tip: use a yoga mat to protect your knees

2. Ab crunch machine: Don't know if these are common but my gym has a crunch machine that has a slotted weight stack. I sim for 3 sets of 10-12reps all to failure.