The Mashable website has a great guide to using Twitter. It is an older article updated about two years ago. Yes, two years is a huge long time in online years. So many things can change in a short amount of time.
I think the key to Twitter is simply using it. Get on. Look around. Have it going in the background throughout the day. It is like the news ticker at the bottom of the screen. If you see something of interest click on it. If you see someone tweet something you like follow them. Retweet it if it is something awesome.