Trouble with scratchy lineart?:
Zoom out to be able to cover the distance between point A and point B with one stroke.Put your line art brush at 93% opacity to make connections look smoother.
(Sidenote, you can color your lineart at any time by locking the layer or putting a clipping mask ontop)
My art uploads fuzzy?:
Make your art at a high resolution and scale it down for the website you want to upload it to. For example I draw at a 4000x6000px resolution and scale it down to 900x for tumblr.
Also want to recommend Waifu2x if you’ve got an image you drew small and want it bigger. This does a FAR better job at resizing than any art program I’ve ever used.