Josei manga-ka (artists) often use a lighter, more consistent line weight – somewhat reminiscent of pencil sketch – that give the pages a very open look and sense of airiness and energy.
Faces tend to have a minimal amount of detail work and, unless it somehow contributes to characterization or expression, physical features are realistically represented. One notable exception to this simplicity is that characters in josei are often drawn with lips (though this depends on the artist) – a feature that is often completely absent from faces in other genres of manga.
Characters in josei often have big eyes. Just not unrealistically huge ones.
While black and grey tones are not absent from the page design, in josei much less contrast is utilized then in other manga genres. The reduced use of contrast gives the pages a more aesthetically calm, representational look.
Settings are often depicted with an eye for balance and economy but are usually very realistic. There are a lot of aspect-to-aspect panels in josei that feature power utility poles. Perhaps josei manga-ka (and, by extension, their characters) spend a lot of time looking wistfully skyward?
Images: series of panels from Nana by Ai Yazawa, photo: Power Pole by Frozen Elephant (flickr)