No one will ever hire me to replace Clinton Kelly on "What Not to Wear" or any of the other fashion related television shows that have become so popular! My wife and daughter have tried without luck to change my clothing style for a very long time. Putting all this aside, I do get questions from job seekers all the time about how to dress for interviews and I ask this question of hiring managers quite often.
The days of following the rule that a candidate must always wear a business suit have faded a bit. The best suggestions I can make are that you want to look professional but not overdressed, conservative but not stodgy, and to appear comfortable however you choose to dress. Of course, the type of job or industry will dictate somewhat how you should look. A machine shop mechanic probably needs to be a bit more casual than a CPA for example but no matter what, you must be well groomed and neat at all times.
For women, coordinated separates are totally acceptable, especially with conservative jewelry and footwear. Avoid wild designs on your nails and streaking your hair with colors such as green, purple, or pink (yes, I have seen this more than once on interviews I have conducted)! It is OK for men to wear a blazer and khakis as long as they are well pressed. Some guys feel the need to douse themselves in very strong smelling cologne. Leave it off on interview days! Also, avoid blazers that are bright yellow or neon green (yup, I have seen this too)!
Basically, neat, somewhat conservative, and tasteful are the rules. Visiting discount clothing stores is fine if your budget is a bit restricted. No one is expecting you to spend all of your resources on your wardrobe!