Disclaimer: I should say that I have worked at marketing agencies for 8 years and in my industry, we walk a fine line between "I tried" and "I'm not boring and corporate". If you know what's expected for interviewees in your industry and what I'm showing is too casual, by all means ignore me!
First of all, if you have a suit that fits you well, then wear it. Your jacket should be able to close, it should NOT make you look like a linebacker. If the jacket isn't slimming, it probably doesn't fit well. I don't like pairing standard button downs with a suit since it can seem super stuffy and boring, so I tend to wear a silky tank or fine knit shell with a fun necklace.
However, if you do not own a flattering suit and will not have occasion to wear it after you are hired, I would not advise investing $200+ when you can look just as put together with basic pieces you may already own. Like this:
For most interviews, it's a good idea to stick with neutral shades and dark blue or green. Even in a creative industry, I wouldn't march in wearing a pink blazer since you never know when you'll run into a traditionalist. I also like wearing the pieces that make up a suit, but not necessarily ones that match, or pairing a blazer with a sheath dress instead of a skirt of pants.
You'll want to keep your jewelry interesting, but not distracting, and definitely not loud. I once interviewed a woman wearing a stack of jangly bracelets and that clinked together as she made gestures and it was really distracting. The fact that I still remember it shows how off-putting it was.
The same goes for shoes - nothing too sexy, and definitely not a pair you can't walk naturally in.
Finally, although it should go without saying, there's always some person who has no concept of where necklines should stop. So I will type it: If you can see any cleavage at all, it's too low. If you can't lean over to pick something up without flashing the room, it's too low. If you have any doubt at all... it's too low.
And with that, I bid you good luck! Stand up straight and remember why you're awesome!