Sure, go ahead, laugh. Writing what’s essentially a status message seems like it would be the easiest thing in the world. But as anyone who writes headlines will tell you, it can be very challenging if you’re trying to convey information and meaning within a very small space. And Twitter, with its 140-character limit, is one of the smallest spaces around.
You will be so dope at counting characters, they will call you Count Floyd.
If you’re drafting a Tweet that’s important to you — an announcement, for example — you’ll want to take into account some factors that can really put the squeeze on your prose.
Spaces count
Remember that the spaces in your message count as characters.
Retweets (may) count
Do you want others to retweet you? Consider cutting your Tweet by 16 characters to allow for an @ sign and a username. (The retweet button on Twitter creates a message that doesn’t shoehorn the original Twitterer’s username into the message, but not everyone likes to use that feature.)
Links count
Will your Tweet contain a link? Check the length of the URLs that the service you’re using creates (bit.ly, ow.ly, Posterous, Tumblr, YouTube, etc.) and make room in your message for it. If you’re drafting a Tweet before whatever you’re linking to exists, leave a placeholder for the URL — ideally one of equal length.
A little Birdhouse in your soul
If you use an iPod Touch or iPhone, you might want to check out a Tweet-drafting app called Birdhouse. I haven’t yet used it myself, but I have it on good authority that it’s a handy way to draft, review, revise, rate, save, backup, publish and unpublish Tweets.
Of course, counting characters is only the beginning. There’s also the small matter of writing well in such a confined space. That’s another post.
Wade Rockett 
Yes – the links are sometimes quite difficult to make fit into the tweet because I don’t like abbreviated URL’s. I like to know what I am clicking on.
Thanks for sharing these tips.
I am drafting a tweet announcement for a 3rd party, so thanks for the info, especially about leaving spaces for retweets. But I am liking it because we have the same template! and mine is pink.