Confused about which grammar rules to observe when you're limited to 141 characters? Here's a Twitter style guide.
Grammar Girl's Strunk & Twite: An Unofficial Twitter Style Guide (in which every entry is < 141 characters)
» Use proper capitalization. Typing in lowercase doesn't save characters; it's just lazy.
» Use proper basic punctuation. It helps people understand what you mean.
» Don't use abbreviations such as 4U and L8. They make you sound like a 12-year-old (which is bad, unless you actually are a 12-year-old).
» Use contractions whenever possible.
» Shorthand symbols such as >, =, &, and @ are allowed.
» Shortened word forms such as nite and thru are allowed (except for Grammar Girl). rationale
» Use numerals, not words, for all numbers.
» Provide links and context whenever possible. Remember that many of your followers can't see what you are responding to.
» Use tinyurl or http://is.gd to shorten links.
» If you can't say it in 140 characters, reevaluate whether you should be posting it at Twitter. rationale
[Note: Grammar Girl will not respond to grammar questions on Twitter that take > 1 minute of research. Complex questions are for the show.]
Credit for the name "Strunk & Twite" goes to Cathleen Rittereiser.