In no particular order:
1. Use one space. Normally, you would have two spaces between each sentence.
One space. One space.
Two spaces. Two spaces.
Use one space to save room!
2. Symbols rock! $ = dollars, & = and, etc. Really helps.
3. Abbreviations are OK. B-day = birthday, etc.
4. Smileys! To show that your are happy, use :), instead of "I'm happy!".
5. Multiple twitters are no problem. Make a twitter for gaming, then another for work, then another for magic.
6. Don't sign your name. They already know who you are, hopefully. No need to sign your name or initials.
7. Wording helps. If you've ran out of room, word your words-haha-and move them around to make it work.
8. While grammar and spelling are usually important, it's alright to use "u" and "2" on occasion.
9. Little punctuation needed. Take away that comma or semicolon when you're seperating something, this isn't the grammar nazis (But they're the grammar teachers, so don't go crazy with the bad grammar and spelling)!
10. Use TinyUrl to shorten your links-or some other redirection service. Also, only post links once or twice in a twitter or a set of twitters. Arctic, my friend, helped submit this one.
Bonus: I have some more material over at tinyurl.com/a3av and tinyurl.com/22uwsg. Arctic, my friend, helped submit this one. :D
Thanks! Peace!