Suit
The best choice for an interview is a two piece matched suit, even if the job is in a non-suit-wearing work environment. Wearing a suit to the interview shows you take the interview as a professional meeting. If the interview include going to a work site where a suit would be inappropriate or the industry would frown on a suit, ask the employer directly and politely or look for advice through professional organizations.

Colors
Navy, dark gray (and black for women), in other words conservative colors, will be appropriate. Black for men was once considered severe or overly formal, and may still be considered so in very conservative industries, although it is commonly worn by many. Other color trends are also possible but avoid the extremes.

Fabric
Choose solids or very subtle weave patterns or plaids. The best fabrics in all seasons are wool and wool blends. It is also acceptable for women to wear good quality micro fiber. Both men and women should avoid acetate or rayon blends.

Cost and Quality
For a job search you should have one good quality suit at least and vary your shirt, blouse, tie, and accessories.

Details
All parts of your clothes should be clean and well pressed. Examine everything for tags, dangling threads, etc.