A standardized business casual dress code would definitely end much confusion for many people. What clothing one company considers acceptable attire, may be deemed inappropriate by another.  Observing what your coworkers and managers wear as well as following common sense instincts will help you on your way.

General Principles

When deciding what to wear, keep in mind what type of activities will be done that day. Who will you be meeting with or seen by? What kind of professional image do you need to be projecting?

Business attire should be appropriate for any chance meetings. Unless at a company‘s social gathering, the attire shouldn't look like it belongs at a party, sporting event, or picnic. In all cases, the clothing should be clean, wrinkle-free, stain-free, and not be worn or frayed. Baggy, skin-tight, or clothing that reveals mid-riff, undergarments, and cleavage should always be avoided.

Religion, politics, and any discriminatory issues are considered to be controversial topics, so avoid wearing clothing that expresses these themes. Profanity and other forms of obscenity are offensive, so avoid displaying these as well.

Appropriate and Inappropriate Attire

Following are generally accepted guidelines followed by many companies:

Slacks/Pants

Appropriate- khaki or dark pants, Chinos and Dockers
Inappropriate - jeans, bib overalls, sweatpants, wind suits, Bermuda shorts, short shorts, or any pants/slacks that show undergarments.

Dresses/Skirts

Appropriate - knee-length or longer; split skirts
Inappropriate- evening gowns, house dresses, skorts, mini-skirts, dresses or skirts short than 3-4 inches above knee.

Shirts/Blouses

Appropriate- button-down shirts made of non-transparent material, sweaters, turtlenecks, and golf or polo shirts (if company approved).
Inappropriate- t-shirts, collarless shirts, sleeveless shirts or blouses; shirts and blouses that reveal shoulders, bare back, mid-riff, or cleavage or that show undergarments; shirts with any logos, slogans, or inappropriate graphics (only company approved shirts with company's logo should be worn)

Footwear

Appropriate - should be made of leather or other suitable fabric; usually flats, dress sandals, open-toed shoes, clogs, loafers, leather deck shoes and boots are acceptable, but it depends on the type of work environment and activities involved.  Many companies do not allow opened toed shoes.
Inappropriate - flip-flops; thongs; sneakers; slippers; other types of athletic shoes (unless company approved)