Im going to share some tips to draw line art by Paint Tool SAI. First make sure you have PTS at your laptop or PC, if you dont you can check this link Paint Tool SAI English Pack Download
Alright lets start!
Open any picture by PTS
After that set Layer1 opcatity to 50% or lower, like this
After you got good vision you can add new linework layer and start drawing.
Heres some drawing tools from PTS
We will using curve tools to draw lineart, im pretty sure that you will like this tools, because curve tools at Paint Tool SAI so diferent than curve tools at Photoshop or Mangastudio.
First line with curve tools, since this one looks normal and not good enough, so we can use pressure tools to make our line looks better.
And after some minutes doing tracing,
walah its done!
good luck guys!