There are loads of pixel art tutorials around, Pixel Joint is a good place to start. In terms of dev, I’d say start with the pixel art present in Construct, and check out the many examples!
The best advice I can give is to figure out your aspect ratio and screen size as early as possible. Pixels should ideally be kept a consistent size across a project. But also just experiment and find your style. If you wanna keep it old school and stick to NES/etc. rules then that’s great, but there are plenty of modern pixel art games that break the mold and look great for it (and many that don’t) 😬