Inkscape has some pretty cool filters and extensions. One that I use quite frequently is the “Jitter Nodes” extension. In the sunset illustration here, notice the outline of the sun. You’ll see that it is not smooth. Take a look at this tutorial for how to add and jitter nodes.
I’ll mention one other technique I used in the picture. Take a look at my little guy in the kayak. I wanted to give the impression that the sun was sort of highlighting the outline of his silhouette. To do this I simply chose a light color for the stroke and then used the gradient tool, setting the top portion of the stroke at 100% and the bottom portion 0% opacity. Then, I again used the gradient tool … this time on the fill, decreasing the opacity toward the back of the kayak to suggest a bit of mist or fog coming off the water.
I have a couple of tutorials you might like if you want to practice using gradients in Inkscape.
Happy drawing.
Laurianne