When it comes to business dress for an interview, the traditional rules of style are still the best ones. Your look should be simple and conservative, and your interviewing wardrobe should be very basic.  You can wear your entire new hip and trendy wardrobe on the weekends; but for an interview, you need to dress conservatively.
There are many different schools of thought on business dress these days; but in my many years in the corporate world (and specifically in the field of recruiting), I have seen many, many business fashion dos and don’ts.  Therefore, I have compiled the following list of recommendations for dress that will be sure to help you look your absolute ‘business best.’

Men’s Attire
Men’s Suits
Go out and buy a good suit.  The rule that says, “you get what you pay for” holds especially true for suits. A good quality wool suit will probably cost more; but if you buy a traditional version, it won’t go out of style and will last almost forever with regular cleaning and maintenance. The vest portion of three-piece suits can generally be saved for weddings, the red carpet, and special events.
Shirts
A long sleeve white cotton dress shirt is still the epitome of classic dressing.  Although blue dress shirts are quite popular now, I still recommend playing it safe and sticking with white.  Make sure your shirts are very clean; and please, please be sure to iron them … even for circumstances in which you do not expect to remove your jacket because there’s always a chance that you might. As with shoes, you can tell a lot about a man by looking at his shirts; and a nicely pressed shirt will give you a visual edge up on your competition.
Ties
Buy a nice traditional silk version with at least some red in it.  Stay away from ties with large or unflattering stripes or ties featuring your favorite cartoon character.  If you are unsure of the correct type of tie, find a well-dressed guy in an upscale suit department that looks like he owns the place and ask him to help you pick out a tie.  Just be sure to explain it is for an interview and not for a wedding.
Socks
Stick to basic colors, and no argyle.  Socks are simple, as long as you remember to wear a pair that matches each other and your suit.
Shoes
Wing tips, dress shoes, Oxfords, or loafers will complete your look.   Be absolutely sure to shine them; and if you can’t do this yourself, spend a couple of bucks and take them to a shoeshine place.  Yes, I look at shoes; and I’ve seen some that look like they were shined with a brick.
Accessories
No back packs allowed. Opt for a portfolio, notebook, briefcase, or a small computer bag in a black or dark brown leather or faux leather as an acceptable accessory for an interview.   Make sure to clean and polish up any rough spots if you need to though, and no Star Wars (or other such less-than-businesslike) folders.
Grooming
Get a good haircut at some point before your interview so that you look crisp and clean.  Rid yourself of any stray hairs from the back of your neck, ears, nose, etc. and be well shaven when you meet with any potential employer.

Women’s Attire
Women’s Suits
When interviewing for a professional position, a classic tailored suit is something you must have. Choose a solid color such as black or navy blue so you’ll be properly attired regardless of where you’re interviewing.
Blouses
A cotton or silk collared shirt in a color or pattern that coordinates with your suit will do well.  And considering that many executives are married, please button up your shirt and do not reveal more of your chest than you think a hiring manager’s wife would like for you to show her husband.
Shoes
A careful balance must be achieved when it comes to choosing shoes because as with men, much can be told about a woman by her shoes.  So when interviewing, a woman’s shoes should not be too feminine looking, nor too masculine.  There are several reasons for this.  First of all, wearing a shoe that is too decorative can cause a manager to spend more time looking at your feet than your face.  Secondly, while bulkier shoes for women have come into a bit of fashion as of late, they are not recommended for the interview process.  A woman who can balance a confident assertiveness with an empathetic softness can be a strong asset to a company, and a woman’s shoe can often be perceived as a reflection of her ability to accomplish this.  Therefore, a normal ‘pump’ type dress shoe with a low to moderate heel that matches your suit will give you a comfortable and classic business look.  Also, unless you are applying for a position in a casual environment, heel height on the shoe is equally as important. Unless you are an exceptionally tall woman, ‘flats’ or ‘mules’ may cause your dress to appear too casual.  On the other hand, stilettos or especially high heels may not give a proper, conservative, businesslike impression.
Hosiery
Wear hose in a shade that is similar to the color of your skin, and stay away from leg wear that is patterned or has decorations at the ankle.  You may consider support hose if you are going to be on your feet all day.  Be sure to check for runners the night before your interview in case you need to make a last minute purchase.
Jewelry/Accessories
Be very careful when choosing jewelry for an interview.  Of course, a wedding band is perfectly acceptable, but a fist full of large rings will detract from the purpose of your meeting.  So keep rings as well as earrings and necklaces classic and not oversized or overstated.  When it comes to jewelry, think:  reasonable but not obnoxious.  The jewelry should be a complement to you, and people should perceive that you look good, not that your jewelry looks good.
Purses and organizers should be treated the same way and should be businesslike in appearance. Consider a small to medium sized purse for an interview, and leave large oversized purses at home or in the trunk of your car.  Take a moment to spiff up your accessories as well.  Whether you like it or not, dirty purse straps and scuffed corners on planner notebooks will be perceived as an indication of poor job performance.
Although you may wear perfume, please don’t wear so much that it enters the room before you.  Consider that many people have allergies, and if a manager tears up and sneezes through an interview with you, his or her memory of the meeting will be marred.

These suggestions should do well to help you land the position you are seeking.