Welcome to the forum!
Have you yet read the section at the very top of this Nikon section of the forum? Scroll upwards for Gordon's recommendations. If this lens will be used as part of your art studies, it may be wise to ask for advice at your school. Otherwise, perhaps, browse the Portrait, People, and Street section here on Cameralabs forum.
A general recommendation? Try the 35mm 1.8G AF-S, a fixed-focal-length lens in the "normal" focal length range. The wide maximum aperture will allow you to shoot in lower light, without flash, than will your "kit" zoom lens. The wider aperture also allows one to isolate the subject from the background by using a shallower depth of field. I must add the disclaimer that I am primarlly a Canon shooter, and have no actual hands-on experience with this lens. My Nikon SLR cameras use 35mm film, on which 50mm is more of a "normal" focal length.
The Nikon DSLR shooters will, hopefully, soon have more to say.