You should try making the canvas bigger, it's really cramped.
I think when eishiya talks about form he means the bigger, overall picture, how things are connected to create a recognizable shape.
Don't be afraid to darken large areas, it can help bring out the form better than if everything is evenly shaded.
Especially with some selective highlights to bring out the most important shapes.
Here is a tiny reference, if you google Vordt you can find more.

Look at how dark it is around his head, it really brings it out. Although it's not the best example of clear form.