What bubbles said
In all seriousness, the basic rule is: learn to know the company. What did they do, what are there core-competences, who is the CEO (and if possible, who is the guy interviewing you) and show that you did your research. You can place interest into both good things surrounding the company (heard you guys where chosen as one of the "great places to live/work") and the bad ("Heard you guys had some trouble finding good people in sales?")
Also, be honest about what you can do and who you are, following up by what you can do to compensate. For instance you might nog be precise, but you can work extra hard and recheck everything you did.
Last, it's better to over-dress then under-dress. You should be able to make a good guess based on research but when in doubt, show up nicely dressed.