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the first answer is always to study the artists of the style ur trying to emulate. pull some up and learn how they do it through experience. im pretty sure this is how other mangaka learn art styles too but i wouldnt know for sure
early 2000s anime is easy once you learn the rules, too. harsh, saturated cellshading, eyes that are buggy and literally the size of their face, round, mainly undefined heads, etc. embrace the flaws of the style, too - a lot of this art is from an era of the internet when people were still getting used to drawing on a digital format that was either perfected into the sheen of modern anime styles of today or phased out (ex. excessive airbrushing)