Hi, check out MrWrongTubes' tutorial here on YT :
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Also, LavaLamp's guide on Next-Gen Shaders/Textures could be useful :
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These should be a good starting point. The rest is trial & error or else you can look at other's cards in CharaCreator (sliders parameters, bonemod, ...) and from there, learn how they tweaked the default model's face in order to make it more realistic / achieve certain facial features.
Fine-tweaking your model usually requires you to mess with AdvancedBoneMod (ABMX), you can show its window by ticking a box in CharaCreator, under "Plugin Settings".
Here's a guide which shows the location of every body parts, as well as how they are named in-game, that can be tweaked using ABMX :
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Good luck!