Texture paint tutorials?

Does anyone know good tutorials for realistic texture painting? And i really mean painting tutorials. Tutos that i’ve seen only seem to show how to use textures from existing photos, but i want to paint them from the start.

I know i need to make a color,- shadow - and a bump map, plus a texture for the colors, but finding a tuto how to do it properly seems to be hard.

I’m trying to paint a realistic-ish alien face that doesn’t have human skin color, so normal " how-to-texture a face"- tutorials don’t really work here.

So if somebody knows any tutorials or has any good tips about this, i would love to hear it.

I would really like tutorials like that too.