We don't typically speak in 140-character sentences. Nor do we have much experience at writing pithy thoughts. Since tweets are by definition short messages, the art of tweeting requires some practice at writing concisely.
How to Write Good Tweets: Find A Point
Stop before you tweet and really think about your main point. What, exactly, do you want to communicate? Make sure you actually have a point in each Twitter message that you send. This may sound simplistic, but it's the most important advice for good tweeting.
Don't take the tweet box "What's happening?" question too literally. People don't want to know everything and anything happening in your life.
It's okay if your point is to say something funny--people love to laugh--or to share a link or photo, but you should always know exactly what you want to communicate.
If you don't know your point, hold that tweet. Your followers will thank you because most are reading a ton of tweets and grow tired of reading trivial, cryptic messages.
Deciding what your main point is should also help with the challenging process of whittling away words and getting your message down to proper tweet-length. You will find it much easier to carve away extraneous adjectives or quips once you know what you cannot carve away.
Three Rules of Good Tweeting: Edit, Edit, Edit
Once you know your main point, keep revising your words until they fit comfortably into Twitter's 140-character messaging limit. A lot of thought and editing typically go into well-crafted tweets.
Look at each adjective, adverb and descriptor. Is it necessary? Move phrases around, too, seeing if you can find a way to say the same thing with fewer words. Sometimes shorter phrases also read better. The first way we write something tends to be the most obvious, and lively writing requires being less obvious.
Always read and re-read your tweet several times, trying to think if there's a way to make it snappier. Don't let words roll off your keyboard unedited as if you were speaking aloud to a friend.
Make sure your tweet has no misspellings or grammatical errors, too. Those can leave a bad impression that gets amplified in the Twitterverse.
Leave A Little Extra Space for Your Friends
If you want people to pass your message along to others by retweeting it, leave a little room for them to add the "RT" symbol and perhaps their own thoughts. If you leave no extra space, you'll get fewer retweets.
Avoid Awkward or Excessive Abbreviations
LOL and OMG may in the dictionary now, but most abbreviations aren't so well known. They will make your tweets harder to read.
Abbreviations like those used in cell-phone texting also can make your tweets sound less than professional. That may be fine for messaging friends but is less than ideal for work-related tweeting. So use abbreviations sparingly.
Give Them a Little More You
Twitter is a very personal medium, even when used for professional purposes. Your followers chose to follow you, so give them a sense of your own voice--what you personally think about something-- through the tone of your writing. Don't just stick to the facts.
Often you can do this by adding a single word here and there to convey how you feel about something--"yuck" or "ouch," for example. "Oh no" and "no kidding" have a personal tone, too. You get the idea.