Wanna get fun? Lie down on your step - 4, 5 risers, whatever, so that your body is on the step, knees bent, feet flat on the floor. Inter-lace your fingers behind your head or neck. Now, sit up.
Isn't it AWESOME!!?? Totally takes ALL the momentum out that you get with your arms. And of course to challenge yourself, you just hold a dumbell behind the head instead of interlacing the fingers. Fun huh?