No offense intended here to any of these games you mentioned.

My advice is to look outside of BYOND's game library for art inspiration.

Look at professional and indie games that use pixel art as a medium.

All three of the games you mentioned have absolutely awful art.

In the case of SS13, the art has been steadily improving over the years. Some of it is really, really good now, but art has never really been the focus of SS13. It's always about features and content. Art is there just to make sure you can see the features that you can interact with.

In the case of DU and WWA, their art is stolen from dozens of different places and jammed together with no unifying style or palette. They look awful because the art they are using is not meant to go together. It's all just pilfered from all over the place and you just won't learn a single good thing from those games' art.

Do yourself a favor and check out low-fi pixel art. When you start getting the hang of making stuff on the small scale you can start learning techniques to go bigger and more colorful.

The #1 mistake that beginning artists make is trying to go too big too fast. Using too many colors is also a common pitfall. You start trying to put texture in art, and the form disappears.

Just use solid color shapes and learn directional shading first. You'll build your skills so fast that way.

All in the name of constructive criticism.