There are a few rules men should keep in mind when going to a formal job interview:
Suit Colors: Navy blue or a darker gray are good. Some dark brown suits are ok but should generally be avoided. Earth tones aren't formal enough and shouldn't be worn. Black suits are plenty formal but are inappropriately flashy, like something you'd wear to a wedding. Blue suits are usually the favorite.
Pin Stripes?: Pin stripes are ok, but only if they are subtle. They add a touch of flair, show adventurousness and can liven up a gray suit.
Style: Stick to a two- or three-buttoned two-piece suit. Four-buttoned suits may be seen as too trendy and three-piece suits may be viewed as too much.
Fit: Suit jackets should fit so that they can be easily buttoned without any real tug marks across the fabric. The arms should be long enough so that about a ¼ inch of your dress shirt can be seen past the cuffs when your arms are relaxed at your side. If you have a "normal build" (a typical shoulders-to-waist ratio), then your ideal suit size is your chest size. If you have a "distinctive build," then you'll definitely want to get measured by a tailor.
Shirt Color and Collar: White shirts are the safest and most conservative. Cream, almond and pale-blue shirts are also fine as long as they are solid without stripes or patterns. Point collars are recommended for an interview, but spread collars are ok too. Avoid cotton-blend shirts, polyester or any shiny shirts. They should be 100% cotton.
Tie Color and Size: Wear a tie between 2 ¾ and 3 ½ inches wide. They should have a traditional pattern and be made of pure silk. No "trendy" ties or anything made of something besides 100% silk. Your tie should reach, but not exceed, the top of your belt buckle. Do not wear a bow-tie to an interview.
The Knot: Windsor knots are generally preferred at job interviews because they're considered the most conservative. Four-in-hand knots are fine as well. Knots should be neat and fit within the space created by your choice of collar. If you insist on wearing an alternative knot style, choose a white dress shirt with a spread collar that will accommodate it. Lettered tie-tacks are fine, but avoid any religious or political insignias.
Shoe Color and Style: Interviewees should wear black, oxblood or brown leather shoes. Black shoes are strongly recommended because they match almost with any suit and are easy to coordinate with a belt. Rubber soles are ok if they are low-profile (without noticeable treads). No loafers! And try to have them polished.
Belt: Your belt should always match your shoe color. Have suspenders but no belt buckles.
Socks: Socks should be dark and coordinate with your suit. They should be long enough so that no one can see your leg when you are seated.
Jewelry: Only wedding rings are universally permissible for men. You should remove all other jewelry, including earrings, for an interview. College rings are typically acceptable for younger interviewees. Cufflinks, provided that they are small and conservative, are fine.
Briefcases: A small leather briefcase or portfolio is recommended to carry your notebook and resume. Do not bring a large briefcase or bag with you.
Cologne: Use little cologne, or none at all. Don't smother them in smell.
Hair: Hair should be clean and well kept. Shorter hair is generally preferred. Facial hair is discouraged, although well-groomed mustaches are usually ok.