An online search
The company’s website is the best place to start. It shows the company as it would like to be seen and the products and services they offer. You’ll get a feel for the corporate style, culture and tone of voice. Check out the annual report and look for a press or company news page.
You’ll see various research and general advice concerning what best to wear for job interviews. The sort of clothes, styles, colours, shoes, make-up, accessories, etc., are likely to have the best effect. Standard rules for dress code at interviews are mostly common sense: be smart, coordinated, clean, tidy, relatively under-stated – however you can go further than merely adopting the standard recommendations to wear blue or grey suits, black shoes, white, cream, pale yellow and pastel colours for shirts and blouses; and to avoid black (too funereal – unless your interview is with an undertakers), bow-ties, Elton John specs and deer-stalker hats.