Something like the artificial example:

RT @whomever: I've got a retweet and I'm not afraid to use it. LOL! http://youtu.be/ABCDEFGHIJKL

You’re manually retweeting a tweet by whomever and the RT prefix and username has pushed you over the 140-character boundary; you’re probably manually retweeting in something like Tweetdeck because the Twitter-native retweet doesn’t have this problem, but then nor does it reshare the tweet on Facebook and other places nor permit editorialising.

So what do you do to get space back? Approximately in order, this is my approach, until sufficient space is reclaimed; it’s sorted for my simplicity, not maximal compression, and sometimes you will want to skip suggestions where they destroy clarity.

1. Lose the space after the RT:

2. Replace and with ampersand

3. Replace your with yr

4. Replace would with wd

5. Drop trailing punctuation where it leads into a URL

6. At this point, it’s probably worth going on a hunt to check if there is any double-whitespace to remove

7. Replace first with 1st (etc)

8. Apostrophise would not into wouldn't

9. Finally, recompress the youtube line using a shortener which produces shorter output, eg: goo.gl

I tend not to replace at with at-signs for fairly obvious reasons, but in a pinch it does save an extra character if you are happy to have @ with spaces each side to prevent username confusion.

This is one of those postings which almost invites people to tell me I’m doing it wrong – and that’s fine, in fact I have a perl script which tweetshrinks messages for me, automating most of the above and saving me from much hassle, and there are webservices which can do the latter too, although the results can leave a lot to be desired:

which cn do the latter 2, altho the results cn leave a lot 2 B desired

…so the above just reflects my manual process, which is often faster than faffing about with other tools.