Maybe you are thinking, "What does email etiquette have to with business development?" Generally, quite a lot. People will judge your ability to communicate, your responsiveness, your diplomacy, and your organizational skills by how you handle your email. Here are a few guidelines that may help you identify where you might improve your personal brand and your client service. Disclaimer: The author is guilty of violating most, if not all, of these guidelines at some point in time. It's not easy to get it right all the time, but it is definitely worth a try.
Make subject lines clear and concise and reflective of the message. Often when searching for messages or after moving them into folders, the subject line becomes very important. If you have another topic to address with a person, start a new email. Don't reply to one that has a subject line that is not at all related to the subject of your new email. This keeps everything neat and tidy from a search standpoint and prevents having multiple topics mixed together.
Use punctuation wisely
Have you ever received one of those emails with exclamation points lined up behind most of the sentences? "Hello!!! Just following up to see what you thought of changes I made to the contract??!!" It makes me wonder if the person sending it has had a little too much caffeine. Punctuation is important, but use it in moderation.
Humor is hard
Humor sometimes gets lost in translation with emails. So, unless you know a person fairly well, and are sure that when you make a joke he or she will know it is a joke, it is probably best to not do it in an email message.