What are good abs Exercises?

I am 5’10, 160 and have a small belly. Everyone tells me that I could convert that small belly into a six-pack very easy because I am not fat. But I only know cruches and sit-ups. I been doing those for a while and below my belly, never improves. Need some advise on abs exercises (lower and higher)? How many reps should I do? Do proteins work? Can you over-work your abs like other muscles? Hope to hear from someone soon. Thanks.