It will take hundreds of attempts to feel like you've learned anything and when you get there you'll still be caught up in how much further you could go. Don't stress too hard if this was your first really successful digital painting.

The lighting fazing from more severe to less severe doesn't bother me to be honest, I figure he's sitting in front of a device and judging the way the lighting falls based on envisioning that 3D scene in my head. That's a big thing in learning to light, considering the scene as a stage, even while you render it in 2D. I figure his pants are getting hit by a different light source. But ideally you decide those things in advance and light because you're assuming a monitor's there or a window's there. Consider the other impacts of that light source in that space. Is there dust in the air? Is there reflective objects? Is there color bouncing from one thing to another when light hits it hard?

If you use Clip Studio Paint use the blend tool liberally. :) It's much better than Photoshop's.

And if you like sketchy don't let anyone beat it out of you. :) It can be applied well.