Being a professional means you must dress for the part. Casual clothes convey an image that you're not taking the job seriously. That's why the professional dress of choice for men and women in the office remains a combination of conservative suits and separates. The clothes show you mean business and that you're serious about your job.
The standard foundation for a professional men's wardrobe is a solid or pinstriped suit in navy, black, gray or charcoal. The suit must be worn with a dress shirt that can be a solid color or pinstriped. Shirt colors must be conservative, such as white and light or medium blue. Ties should be conservative, not too wide or too skinny, in silk fabric that is a solid color or features a small pattern or stripes. Socks must rise to the calves so that when sitting the ankle is not exposed. The classic dress shoes are lace up oxfords or shiny slip on loafers.
Women's professional clothes are very much like men's. Dark, conservative suits are best because they are formal and dignified. Skirts and slacks are both acceptable. Lower heels are the choice for the office in either pumps or slingbacks. Soft, smooth exposed legs are great at the beach but unpolished at the office. Cover them up with sheer stockings. Blouses should be conservative as well, and V-neck blouses and dress shirts work best. Jewelry must be limited, small and not distracting. Scarves are acceptable if they are tied neatly and the print is not too loud.
Many offices allow casual clothes on Fridays. However, this is not a license to wear jeans, shorts and T-shirts. Casual clothes for the office mean dressy casual clothes, just like you'd wear to a nice restaurant. For men, that would be khaki slacks, a button-down or dress shirt without a tie, a blazer and loafers. The look is the same for women, although you can substitute a skirt for the khakis and substitute a cardigan set for the blouse and jacket. Heels are still a requirement for skirts. Women may wear slacks with loafers on casual Friday. Check with your company's dress code for casual dress guidelines.