Twitter has grown in popularity as a way that people keep up to date and interact. Specifically, it's use has been incorporated into promotion and updates regarding events due to the broadcast nature. When to Tweet - Similar to when you might post on Facebook
Tip: Get a shortened URL for your Tweet - Since you only have 140 Characters for a tweet, you may want a short URL to use in your tweet. From the 'Get a Link to send friends' in the 'Get Involved' section of your event. The added benefit of using this link is that there will be 'click' statistics automatically generated for it.