When you make a digital document - either photoshop or SAI or whatever - make sure the dimensions are decently large (I often use the standard 8.5 x 11 paper size as a starting point) and make sure the resolution and dpi is decent. Often times programs will automatically set the dpi (dots per inch) to 72 (even photoshop does this), but try setting it to something like 350 or 600. I guarantee you will see an increase in line quality, as in 72 dpi, it means that things will get blurry a LOT quicker as you zoom in, and there's a lot less room to make lines look sharp.
So ya, whenever you make a new document, just check the dpi settings (it should be there in new canvas settings no matter what program you're using) and see what it's set to. It might make a difference setting it to something higher. I use 350 dpi for Uzuki, if that means anything
I agree with this u o u one of the reasons why I prefer SAI over Photoshop (besides it being more user-friendly and less of a heavy program on my computer) is because the line quality is just -better-, and you don't need those filters and stuff to make it look nice. The colors in my strips always look so vibrant and sharp when I use SAI to paint u w u