Practise. Lots and lots of practise.
Smoothness in lineart has a lot to do with confidence, which means putting in the practise will help! Getting used to the intuous will help too, but mostly it's putting in the practise to the point where you learn to stop worrying so much. Just open a new blank canvas and practise drawing lines with whatever tool you use for inking - and try to do longer lines! Breaking a habit is hard, so you have to put some conscious effort into it.
Also, it helps to move your whole arm when you draw, instead of just your wrist. When you're drawing a long arcing line, try to move your entire forearm from your elbow on down, instead of just moving your wrist. It will help keep the line steady, and will also put less strain on your wrist.