When you write emails for work you have to treat them like any other professional document. They are a reflection on you and your business and once you've sent them you've lost all control over who sees them and how they are interpreted and used. THINK BEFORE YOU EMAIL.
#1. If you need a response only send to one person at a time.
Asking six people for help in an email will frequently result in none of them replying. ie. "We need to bring food to Friday's office meeting." Response? Nobody will bring food. Each person will see the 5 other recipients and assume one of them will bring food instead of them. To remedy this I recommend making the email more personal (as opposed to talking to an audience) and BCC it to everyone so each person thinks its just for them: "Can you bring some food to Friday's office meeting? I think it would be beneficial." Also this is pretty much a necessity when discussing anything confidential or potentially embarrassing. (If you want an immediate response you're better off just phoning the person.)
#2. Limit each email to one topic or idea.
If you've ever received an email with a list of different topics to respond to you know it takes significantly more time to answer such an email. Indeed you are much more likely to put it off until later because you want more time to think of a proper response. You immediately recognize writing a proper response will take an hour or more and if you already have a busy schedule it will have to wait until later. Thus when sending emails its better to send multiple emails which can be answered quickly and individually.
#3. Change the email's subject.
When emailing back and forth the subject you are discussing will sometimes change. When that happens its best to change the subject line, especially if you're deliberately changing the topic. This keeps the conversation clear and logical (and avoids confusion). This also makes it easier to find the email again later because you will remember the subject header of the email.
#4. If you wouldn't say it in person, don't put it in email.
If you're not sure if something is appropriate conversation (or important) ask yourself whether you'd ask it in person. Thus things like flirting or insulting your supervisor in a funny way is probably a bad idea. THINK BEFORE YOU EMAIL.
#5. Stop Laughing out Loud so much!
LOLs are actually annoying to many people, but more so are the people who use them repetitively. Try to avoid using it too much (or avoid it altogether). The same thing goes with smiley faces and other emoticons. ChatSpeak is not appropriate for professional documents. The same goes with slang and excessive foul language.