I really like this style! It has this kind of classic-retro feel to it that is very appealing. The only thing I really noticed is that for the black-and-white girl, her head and neck seem to be on the large side in proportion to the rest of her body. Hands and the flowiness of the clothing could also use improvement but that's something that gets easier with practice-- just try and draw clothing and hands from photos or other good reference materials. Learning a bit about how clothing is constructed (where seams go and so on) also helps you draw it more easily.