Concision

The general rule in most things is "more is less" and that certainly applies to Facebook. It's not like Twitter, you have as many characters as you possibly want (I think). However, do you want to read a novella on someone's wall? I certainly don't. The important thing is to keep things short as often as possible. Of course, this isn't an "always" rule, sometimes you just need to post a little more when something especially awesome is happening. Of course, don't ramble on forever. Here are some tips for keeping things as short as possible. (List and examples from Colomb & Williams' Style)

1. Delete meaningless words - These are words that don't add meaning to your post but instead get in the way. These can include: kind of, actually, basically, generally, given, various, certain. However, Facebook is more informal than traditional discourse and more conversational in nature, but when writing a long status, think about omitting them.
2. Delete doubled words - By removing any words that repeat meaning like "full and complete" or "any and all" you can apply some much needed concision to your statuses.
3. Delete what readers can infer - This includes redundancy and just annoying repetition like "terrible tragedy" (that is why it's called a tragedy, right?), "future plans," "true facts," "final outcome," and "basic fundamentals."
4. Change negatives to affirmatives - By expressing ideas in the negative, you often are adding words but are also asking the reader to interpret what you mean. Most negatives can be rewritten such as "not careful" becomes "careless" or "not include" can become "omit" or "remove."

Bonus points! (Do these and be extra spiffy!)

1. Replace a phrase with a word - This requires a rather large vocabulary in order to do this, but if you can, go for it! Examples include changing "carefully read what you have written" to "edit" or "sequences of subjects and verbs" to "clauses." (Okay, that wasn't so bad...) 
2. Delete adjectives and adverbs - This is hard to do in a more conversational or informal tone because they all feel SO necessary, but try taking them out and see how quickly your prose streamlines!