I see a lot of art. As en editor and creator, I see a lot of art. In seeing a lot of art, I see a lot of the same mistakes that artists make over and over again.
The biggest mistake is thinking bad anatomy is actually style. No. Just stop being lazy and go learn how to draw. (This is mainly for superheroes.) Mistaking bad anatomy for style is lazy, and it means you aren’t ready for paying work.
Perspective and planes are also big things. Vanishing points. These are the “simple” things that artists need to know. These are the basics. Just as writers (should) know spelling, grammar and punctuation in order to begin to tell a story, the artist should know anatomy, perspective, planes, and vanishing points.
Now with that out of the way, the next biggest mistake artists make is not taking the dialogue into account when they start laying out pages and panels. And I see it time and again.
Panels need to be laid out in such a way as to leave dead space. This is where the copy (dialogue, captions) will usually go. If there’s no dead space, then the copy will be directly on the important parts of the panel, and that’s not where it’s wanted.
This mistake is generally made by newer artists. More seasoned artists don’t make the mistake because they’ve learned, possibly the hard way.
As an editor, I love seeing thumbnail drawings where the artist has also incorporated blocking for dialogue. To me, it means they’ve not only learned, but they’re also thinking about the other people on the team, mainly the letterer and the editor. (And redrawing things puts strain on the deadline, which is never fun.)
Artists, do yourselves a favor: incorporate ideas as to where the dialogue is going to go when you’re laying out the panels. That will go a long way into helping you make better decisions when you draw.