There are plenty of ways to make yourself actually smarter, but if you're just looking to project intelligence, The Wall Street Journal has a handy venn diagram that shows what we do that actually works.
We do a lot of things that make us think we look smart, like putting on a very serious facial expression, or using complex words. Those don't really work though. Instead, it's actually best just to be clear, concise and engaged:
The observers also gave higher IQ ratings to participants who appeared more relaxed and confident. They rated as smarter participants who wore a self-assured expression rather than a poker face, spoke clearly in a pleasant, expressive voice, and were responsive to their conversation partners — gesturing, nodding and "being engaged in the conversation and paying attention," Dr. Murphy says.
As you'd expect, there's a lot more to it than just a quick diagram, but the key points remain the same either way. Head over to The Wall Street Journal for the full article.
How to Look Smarter [The Wall Street Journal]