Hash Tags help people find your tweets on specific topics. They are a way of adding meta-data to your tweet to group tweets of a similar topic together. Use a # mark followed by any word, with no spaces, such as #swineflue. Special search engines like Hash Tags index and organize tags and help spread your tweet around.
TweetDeck is a desktop client that helps you manage twitter. It separates our your general tweets from those you are mentioned in from direct messages. It checks for new tweets on a user adjustable schedule and has a discreet onscreen notification when something new pops up.
Twitter Search do a quick search for your topic to find new users to follow.
bit.ly sure there are a lot of URL shorteners out there, but bit.ly also features link tracking. Sign up for a free account and start collecting metrics on the links you publish in your tweets.