Try to make your point in the opening sentence. Grab their attention first and then add intricate details in the next few paragraphs.
Most emails should be limited to only a few paragraphs, use attachments for submitting larger amounts of data.
If you want to address more than one topic then use more than one email. This will make it easier for everyone involved to sort, file and recall it.
Use the subject line to your advantage. You may wish to use your name and an interesting topic.