Hi! Welcome to Twitter - I avoided it for the longest time, but find I'm really enjoying it now and know I've had at least a few sales directly from the site plus have made a lot of really great connections.
ThisSticksLife is right - definitely don't use it to just drop links all the time... you'll get the most out of it if you engage in (140 character) conversations.
Some basic tips:
-Include a profile picture - the default image is ugly for a reason, Twitter wants you to change it!
-Include a bio about you, not necessarily about what you sell (include a link to your shop or blog though) - what can other people expect you to tweet about?
-Learn the lingo...
... Use @ at the beginning of a tweet to reply directly to someone else
... Use @ anywhere but the beginning of a tweet to mention someone else
... RT means that something was "Re-Tweeted"
... Using # turns the word immediately after that into a hashtag, a clickable link that will show other tweets with that same hashtag
-Update your background image - I made mine coordinate with my Etsy shop to keep things consistent, but you can get creative with it.
If you're interested in more info, I blogged about my top 5 favorite tips today to help make Twitter a bit less overwhelming for newbies -
http://saltcityspice.blogspot.com/2011/05/top-5-twitter-tips-for-stress-free.html