The "Secret" to Beautiful Hair. (har! har!)
Like regular inking, for long, smooth lines, you want to make sure not to rest your hand on the drawing surface. Draw with your arm and elbow motions instead of your wrist motions. However, here's another neat little trick you can do for digital inking and getting those beautiful, sweeping, yet controlled lines:
Try lightly resting your pinky on the surface while inking. Since there is no ink to smudge, no rough paper to catch, and a tablet surface is incredibly smooth--with a little practice, this technique should give you increased control over the smoothness and weight of your lines. Your pinky (and the fingers resting on your pinky) act as a sort of spring with which to control your pressure.
Lots of people ask me "how do you draw your hair?" (actually, that's THE most asked question I recieve) Well, that's it. This is the technique I *always* use when drawing hair, the curve of bodies, and sometimes clothing. Sometimes I'll even put a little piece of paper under my pinkie if it's a humid day out and it won't slide on the surface like it usually does.
And there's actually a little bit more to it to that, but I can't go giving all my secrets away, now can I? Making digital inking look completely natural is a challenge you'll have to learn on your own. Everybody discovers different techniques that work for them. That's the whole fun of it all! :)