You want to make sure that your clothes do not have any wrinkles or stains on them. Pick an outfit that best suits the type of job you are applying for. If you are going to work in an office setting, you should dress conservatively. A nice dark suit is good for men. Soft earth tones are best for women. Try to avoid mini skirts and shirts that show too much skin.
If the job is outdoors or in an artistic environment, you can dress a bit more casually. Just be certain to avoid wearing denim jeans, over-sized clothing, and under-sized clothing. Ladies - try and avoid wearing too much make-up. It gives the wrong impression.
Even in the summer, you should not wear sandals, flip-flops or gym shoes to an interview. It sends an unprofessional message. The same goes for hats and other accessories.