Always start with a greeting. This is important on all responses...even if this is the 3rd or 4th time you've responded to the customer. You can change up your greeting to prevent the messages from becoming stale or monotonous. 

Paragraphs are a collection of sentences about one topic or theme. Please break up separate topics into different paragraphs. 

Avoid run-on paragraphs. These are paragraphs that just keep going even though they contain details on 2 or more separate thoughts. 

Use a full empty line between paragraphs. 

Avoid using more than one empty line consecutively.

Avoid using tab or indentations. Keep everything left-aligned.

Delete any empty lines at the bottom of your response so that the automatic signature is placed properly.

Avoid pasting a long list of details into the reply; this will be difficult for the customer to traverse.