Twitter is one of the most powerful tools a teacher can use. I use it both professionally (@VickieMorgado1) and with my students (@MrsMorgado1). It has allowed me to connect with educators all over the world and learn from them. As well, it allows my students to connect with other classes and learn from students in other countries. You can see examples at our Twitter feed.
Here are some resources that are useful to get you started:
Twitter in the Classroom
Twitter in the secondary Classroom
CNN Report on Twitter in the Classroom
Twitter Tutorial Video Created by Students
As well, you can use Twitter to form a Professional Learning Network. Follow other educators all over the world or participate in educational chats. Here is a great video by Victoria Olsen to get you started.
Here is a list of Educational Hashtags (#)