Just don't worry about getting the lines all perfect in one go; usually what I do is make a bunch of lines for one curve (for example, if I'm making the neck, I'll do it in three different parts) and then erase the bits that poke out where the lines cross, and then smooth it a little more. I don't know how to explain this any better, so let me know if you need any pictures of this.
Also, changing my pen brush settings in SAI a little bit seemed to help. I usually only keep my stabilizer at 5, and make the minimum brush size a lot bigger, like 60%, so the brush doesn't taper off a lot, and change the quality to 4 (smoothest). That helped me on the lineart for the picture I just finished, and I think I'll keep it that way for a while. If you could be a little more specific about what you want to change or fix about your lineart, I might be able to help more your lineart looks great to me already but I get that sometimes people just want it to look the way they see it in their heads, not just make what other people like