You can find many different resources online that talk about successful tips in composing business emails. A simple web search might be immensely helpful here. I think that one of the most direct approaches would be to maintain proper grammar and writing skills. It is important to not compose emails with the same technique that text messages or Tweets are composed. "You" instead of "u" or "Later" instead of "l8r" would be examples of this. It takes away from the business format when the message is a casual text and not a direct business communication method. Along these lines, spellchecking your email would also be a very good step to take. Emails that are filled with mistakes of spelling and composition present themselves in an unprofessional manner. I think that the use of the "Subject" section of the email can also be an important element to add to the professional nature of the business email. Being able to provide a pertinent, direct, and meaningful subject heading in a succinct manner can allow for focused communications with clients or colleagues. This can help to facilitate a proper business sense to your emails.