1:The textures have no details such as gathers, pleats, pockets, buttons, seams, laces, hems, etc (or details like bellybuttons and muscles on skins). Try opening some EA or nice custom textures and taking a look at the details on them for inspiration.
2:The textures have some details, but those details are sized or placed incorrectly. Clothing should not stop abruptly at the neckline, sleeves, or other edges, and gathers, pleats, pockets, buttons, seams, laces, hems, etc., (or details like bellybuttons and muscles on skins) should be scaled correctly and placed in the right location, and should fit the mesh used.
3:The textures have some details, and the sizing and placement fits the item and the shape of the mesh.
4:Your textures have nice details with everything correctly sized and shaded. Yay!
5:The details on your textures are exquisite, with everything sized, placed, and textured just so. Excellent work!