You'd be able to self-critique 1000% better if you took even a single class under a good instructor. Even self-taught artists made the effort to message artists better than them, the worst they can do is ignore you.

While >>7714541 is ultimately the best you can do, here's some actionable steps you can take today:

Watch videos of instructors critiquing their students work. Odds are that you're doing the same thing they are and it'll help you see.
Move around to look at your work from different sizes and angles you'll probably see more problems.
Come back to something you've made after a day or a week, this will give you a fresh take on what you've made.