Painting digitally is definitely a nightmare when you first try it; there's so much to figure out and it's all so confusing. For lineless paintings, I start with a rough line sketch, and I try to transition to the painting part as soon as possible, so any more work I do will look good without the crutch of the line sketch.To get that smooth shading look, I use the airbrush tool a lot, and lately I've been using Photoshop's mixer brush on the Wet setting to blend my shading. It's basically like the blend tool on other programs. Some blending is just elbow grease too, like shown here: vetyr.tumblr.com/post/15881837… Keep at it and you'll get better and better. I still haven't "figured it out" fully, but I'm doing stuff better and faster than even a few months ago. Good luck!