Impress Someone With Your Intelligence

You want people to think you are smart! The easiest way to do this is to specialize.

Steps

Choose a small area in which to become an expert.
Read books and magazines about this topic.
Find other people who like this area too, and spend time with these people. The conversation will inevitably lead to your favorite topic, and you will therefore learn even more about it.
When you are with the person you are trying to impress, steer the conversation over to your area of expertise every once in a while. The more you know, the more impressive you are going to be.
Study History. Studying history will give massive amounts of general knowledge to draw on in almost any conversation.

Be sure to learn all the vocabulary and buzzwords associated with your topic. If you like cars, know what a V-8 engine is, for example.
A good way to find others interested in your topic is to join a club. If birdwatching is your thing, start going on those Saturday morning hikes you have read about in the paper.
When you try to impress someone with your intelligence, be sure to find a person who will respond well to your area of expertise.
You don't have to know a lot about everything to show that you are in fact quite intelligent. You just have to know a lot about any one small area. Not too many people can tell the difference between a Gypsy Moth and a tent caterpillar, but if you can, people are going to notice!

Try not to make your knowledge too obscure or uninteresting to others. Don't specialize in something like the manufacture of ballpoint pens.
DO NOT look like a know-it-all because nobody likes them.
Sometimes people are put-off or feel belittled when talking to someone who is trying to impress them with smarts. Be modest with how much you throw at the person all at once.
If you try to impress someone, who doesn't play computer games, with your Marvel vs. Capcom 2 knowledge, you'll come off looking like a geek. Pick your targets with care.
Never try to impress anybody with a topic on which you know very little. You might end up with embarrassment if the person you are talking to knows more than you do and correct you when you went wrong with any of the information.
If your target knows nothing about this subject, it really isn't worth it.
All of the above are merely a bunch of tricks to make fellow dumb people perceive you as smart. Over the long term, the thing to do is BECOMING smart, not pretending it. Study serious subjects, try to get your world-view as broad as possible, have some genius idols(e.g. Richard Feynman) and be very humble with your knowledge (Socrates: The only true wisdom is in knowing you know nothing).