1) Dress for the role - Interviewing for the CEO role? VP of Sales? Wear a suit, executives wear suits. You want to be a big shot you've got to look like one, in this case wear the suit and make sure it's not "dated". No one wears a 3 piece double breasted Olive Green suit anymore.
2) Know the company - Don't show up assuming a suit is appropriate. Take some time, do some research. You don't want to show up and be "that dude in the suit" who everyone wonders what/why you are interviewing. Many companies are "business casual" now, meaning you'd NEVER wear a suit to work.
3) Be comfortable - Can't stress this one enough. You may be in a 6 or 8 hour interview, you've GOT to be wearing something that you can be comfortable in for the whole day. I know personally, wearing a tie is brutal for a few hours, so if I can avoid it, I do!
4) Ask somebody!! - Seems like common sense, but ask someone. Ask your recruiter, the hiring manager, your buddy in accounting.....doesn't matter. Take a few minutes to find out the inside scoop and plan accordingly. Take advantage of your connections to make sure you look the part.
That's about it......don't just assume you need to wear a suit or even a tie in your interviews. Those days are over for most employers (finance, legal, C-Level, excluded of course). Remember, it's not about what you wear, it's about how you interview, communicate and your fit for the job.
Good luck, sorry for the short blog been battling a cold the last week....