Anchor your feet under something and lean back until you feel your abs turn on. Try to keep your spine and neck as neutral as you can. You can go light and do the exercise for 60 seconds, or use heavier weights and shoot for 12-15 reps.
Maintaining the half sit-up position while performing any movement with the arms will challenge the abs, hip flexors, and even the neck muscles.
Are you doing any dips variations? You should be. Here are some interesting options, including straight bar dips and Korean dips, to jazz up your training.
So you think you know how to do plain, simple, Incline Dumbbell Curls, huh? Well maybe you do, but there are at least a couple of trick you can pull to make the movement a whole lot more effective.