When you work, make sure you keep a preview window open so you can see your art at 1x or 2x zoom at all times. A lot of colours and details that might seem like a good idea when you're zoomed in don't actually show up well when you're zoomed out. As a result, it's easy to end up with washed out colours where all your hard work isn't even visible without zooming in a bunch. For example, the highlights on the buttons on the coast, the highlights on the boots, and the shading on the costume eyes may all as well not be there, they're invisible at 1x-2x.
Related to this is your use of low-contrast colours. It's easier to see the difference between colours when each one covers a large area. When you're soomed in, everything looks like it covers a large area, but zoomed out, it's all quite small and everything starts blending together. As a general rule, the smaller your art, the more contrast you need to maintain the same readability.
I recommend checking our the forums here and making a WIP thread for some of your work, if you're interested in some back-and-forth, edits, etc. The gallery is intended for finished work, so people are less likely to give specific advice here.