I've seen a lot of people struggle with digital lineart. Luckily, there are smoothing functions in lots of digital art softwares now, not just the famed stabilizer in SAI. Even GIMP, a free program, has a smoother.
If you have a program with a smoothing function besides the ones featured here, please make a tutorial about it, and I will be glad to link to it.
Here's a tutorial that better explains the stabilizer in SAI. (I have a Mac, so SAI doesn't really work on my computer.)
For mouse users, here's a few tutorials on pen tools in various programs:
If you want to share this tutorial, please give people the link to this page instead of reuploading. Thank you.