I was just talking about this with my spouse, because she can't figure out how I do it. YEARS of experience.
Women in just-barely-fashionable attire that's a tad too long at the knee, but not so long as to be "granny-style." Generally, great care with their hairstyle, but not much make-up and only a little jewelry. Clothes usually are more JC Penney than Wal-Mart, but not always. I've always wondered at why so many JW women make a bee-line for pastels and floral prints (about the only ones with any real color sense seem to be the sisters of color--Latina and African American sisters always seem to be a little better-dressed, or maybe they don't stand out as so different from "normal" to me because of my own cultural biases). JW women also have longer hair (again, IN GENERAL) than women in their age group do in the "real" world.
Men's suits are usually pretty light-weight and plain (also on the cheap side), gray, brown or navy. (Don't see much black ... I wonder why?) Men's shoes tend to be a little scuffed (not replaced regularly). Only short-sleeved dress shirts you see are on the young boys (once you reach a "position of responsibility," you're wearing a jacket!).
I've started to notice that there's less carrying of briefcases and bookbags, and a move to portfolios. I suspect that's because they're pushing light-weight books and magazines (the new paperbacks are much lighter than the old hardcovers). One effect of this is to make JWs stand out less--clunky bookbags were a dead giveaway.
But the dead giveaway? A whole group of people dressed for business standing on a streetcorner talking to each other while holding up WATCHTOWER and AWAKE! magazines. Happens daily in downtown Sacramento, and I always get steamed. My grandmother and aunt used to take me to do streetwork with them, and we actually worked at it--starting conversations instead of just taking up space! I can't believe they get to count time for just standing around! (And this is the point at which my spouse always laughs at me, getting pissed because they're not "doing it right" even though it's a crock from beginning to end.)