I think more than anything, its whether or not you set your brushes up correctly. Using pen sensitivity is vital when it comes to the smoothness and fluidity of lines draw through a tablet. Also, using gaussian blur to smooth, or other blurs also helps.
There are many many factors that come into play when drawing lines, so if you're more specific about what the lines are for and what you plan on doing with them afterwards I believe I could answer more directly : ).
Either way, you can find tons of lineart tutorials around that might help. Most will be for tablets, but you're bound to find a few that'll have tips for a mouse too. The best thing I can tell you to do is just to practice. Find what tools work for you and use them, but everyone does it a little bit differently. So yeah.
I understand. I got mine not to long ago, it is hard to adjust. Something I was told to do was learn to use broad strokes and swiftly make my lines. If you try to draw slowly with a tablet it'll usually come out wonky, unlike a pencil you can control easier. Even the best tablet would pick up extra movement if you drew slow and your line wouldn't appear as smooth. Also, experiment with Photoshop (or whatever program you use) and the tablet's own settings. See what works for you, pen pressure and brush sizes, etc.