Sometimes you need to take two minutes to get mentally set before starting a writing task. Here are a few useful questions to ask yourself to help you keep on topic, and get the tone just right.
Who is your audience?

• Who are your readers?
• Why will they be reading what you write?
• What will they know about the topic?
• What additional info will they need to know ?

What is your purpose?

• Do you want to: inform, entertain, persuade your readers?
• What major points do you want to make?
• What response do you want from your reader?

What tone of voice do you need?

• neutral
• scholarly
• critical
• sarcastic
• flippant
• chatty