I’ll elaborate more on how to prepare a canvas for pixel art in a separate thread, but I set up this one at 384 x 256 pixels (256 is about the pixel density - on average - of a high fidelity NES or low fidelity SNES game).
Now it was time to drop pixels! There are lot of programs you can use for this, but I use photoshop since it lets me manage/change colors very easily via layer effects.
There aren’t any special tricks here, at least not that I use. It’s kind of a grind, but I just work on carving out the shapes with pixels, using the sketch I created as a visual guide, until the figures look complete. It takes many hours, which is why I like to keep the palette somewhat limited: maybe 2-4 colors for the uniform, 2-4 colors for skin tone, etc. Too many colors or layers can also dilute the sharpness of the pixel art and just make it look like a blurry or lo-res photo.