I've noticed that many nice things happen when you give credit where it's due. This is no more evident than in the New Media, which is all about the conversation. It may seem paradoxical to give credit to someone who may have more followers than you since so many people know them and their ideas, but here's why it's a good idea: if they feel you're helping them, then they will reciprocate by promoting you to their larger audience. Even if they don't, then it's still the right thing to do.
Have a look at my favorites timeline... you can be fairly certain that if I haven't credited someone else, then it's actually my own quote/musing/rambling/whatever. Sometimes the idea may begin with someone else's, but it's only when I feel I've made significant modifications to the idea that I don't quote them.
Similarly, if you're re-tweeting someone, ALWAYS begin their part with "RT @TheirUserName." There are two reasons for this: You want them to see it, and that's the only sure way because it makes the tweet show up in their mentions. And again, it credits them with the original idea. They may continue in a discussion with you for some time if you do this, and each time you're each getting exposure to the other's followers. Always try to have conversation frequently. Pronouncements are good, if the ideas are good, but conversations have benefits that pronouncements do not.
Incidentally, you'll notice that almost all of the tweets I've favorited in my favorites timeline are pronouncements... what's up with that? That's because a favorited tweet needs to stand on its own. Here's why: favorites reach further back in time than anything else you can do on Twitter, and when you go so far back, it's impossible to find the rest of the tweets that were parts of the conversation (unless you favorite them all, which clutters your favorites timeline.) Favorited tweets, as noted, really should stand on their own, which is the essence of a pronouncement. So your favorites timeline likely won't closely reflect the character of your full timeline.
Two more things on format: for non-twitter quotes I hear or read, I've done them in two ways in the past: 1. Begin with "@TheirUserName: " if they're on twitter or "Their Name: " if they're not. 2. End with "~@TheirUserName" if they're on twitter or "~Their Name" if they're not. Each method requires the same number of characters, as you're using a colon after the name on the first method or a "tilde" (or whatever the proper name is for that cool little squiggly dash) before the name. So there's no character burden either way.
I now prefer the latter method, because if you're quoting someone several times (like you may do when they're speaking at an event of some sort) then it gets boring to keep leading with their name. Chip and Dan Heath, in their excellent book Made to Stick, have an entire chapter on "Don't Bury the Lead." It's an old news maxim going all the way back to the Civil War; the upshot is that you should always lead with your most important idea, and spend the rest of the article supporting it. That's why I now prefer to quote at the end rather than the beginning.