Personally I follow this tutorial and I’ve created Actions in PS to save time.
(Scroll down a little bit, you’ll see it)
First thing I do is get rid of the blue sketch by desaturating the image and upping the lightness - but only with Cyan selected. Then I do the Levels to make the blacks blacker and whites whiter. Then Unsharp Mask.
Then I select my lineart, make a new layer, and while keeping the selection up I fill in the new layer with black. After that I clean it up using the layer styles thing to highlight the lineart.
Then to speed things up I use the Magic Eraser tool, since it can clean up lots of the little specs faster. I go back with the regular eraser for anything that doesn’t get and to clean up overlapping lines that look unsightly.
Although some of my steps might be redundant, since tbh a lot of the time the lines just come out too jagged looking - so sometimes I use the Eraser to smooth those out.
Also what I use for sketching is a Pilot Eno Soft Blue Mechanical Pencil. Sure I can only by the lead online but it erases so well and is easier to see than my Non-Photo Blue wooden pencil. Also a MOO eraser. Idk why but it’s so good at erasing compared to other erasers I’ve used.
But most importantly, make sure your scanner is clean. I scanned a business card the other day to make custom stickers for my moms cake business and that scan was so filthy. So hard to clean. And I can’t figure out where all the dust and grime comes from on my art, since when it’s never that dirty when I put it on the scanner. I mean like big things that would be obvious like some random orange goop that wasn’t there before but suddenly is. Tho there might be something wrong with my scanner, idk.
Just make sure it’s clean is alll.