When I give advice to people who want to get into pixel art, I usually give these recommendations:
* Pick a few art fundamentals and aim to study them, by recreating real life scenes or other images with a focus on a specific principle(lots of people will study by recreating the classics). Proportion is one I regularly struggle with because I'll tend to rush along through the early part of the image: if you're drawing figures but don't add enough structure to their proportioning, they will look deformed. But I learned how to proportion better by studying typography, which elaborates greatly on measures and ratios. For any given art principle there are usually guidelines, tricks, and ways to add structure that help in conveying a desired indication without just doing guess-and-check and grinding your muscle memory. And there are a lot of working artists who produce output by grinding through it with the help of the undo key, cut+paste, etc., but traditional forms usually emphasize bringing more preparation to the image.
* Fewer colors are usually better - a principle that is true within pixel art(using more colors usually means you are adding detailed lighting and texture, which can get out of control pretty quickly and doesn't add a lot of information to a low-resolution pixel image) and only somewhat less so in other forms. Paints offer uncanny amounts of smoothness through blending, but this also means having to manage a nearly infinite number of values. Folks who really want to convey perfectly accurate representational scenes these days are likely to look towards the gamut of digital tools to help manage or automate these considerations, since fighting them with traditional materials can be so time-consuming.
* In terms of specific techniques for making marks or stylizing the image, they do depend a lot on the medium, but you don't need a lot of different techniques to do good work. For pixel art, I often suggest following castpixel's[0] style, which is to always make pixel clusters of two or more. This is a style that forces the indication of "brush strokes" throughout the image and makes it easy to resolve fine details, though it sacrifices smoothness around edges.
Across all the arts, the creative part often takes the form of setting down a few broad conceptual rules and structures intended to communicate the idea, and then the remainder is an exercise in the technical followthrough of those rules. So don't feel too pressured to follow a specific set of rules or techniques, as long as you execute consistently through the piece. As a hobbyist you're totally free to explore any combinations that come to mind, even if they're "inefficient" or "unpolished" - you don't have clients waiting on you!
[0] https://mobile.twitter.com/castpixel/status/1006437480059596... (she's talked about style in more depth, but you can see the clustering rule pretty clearly in her work)