Don't overuse emoticons, or they get annoying. One per paragraph is a lot. Remember that these symbols grew up in informal conversation. Correcting someone on their use of smileys, etc. would make you look like a grammar nazi. Remember, you're talking with real people at the other end of the modem line.
Some people post to the Internet like they're scribbling on the men's room wall.
Some of them are even older than seventeen. Make an effort not to follow their example. Think about what you are saying and reread what you send. Don't assume that everyone who reads what you say will share your basic beliefs and assumptions. People from all over the world are on the Internet.