1. Clarity
It must be incredibly clear for the reader.
2. Simplicity
Don't get wordy or use too many adjectives.
3. Brevity
Short words are better than long words; Short setences are better than long sentences.
4. Humanity
Be yourself.
Bonus Tips:
No Self Importance
It's not about you (Unless you're writing about yourself).
Keep It Conversational
If you write like you speak, your message will be more interesting for the reader (unless you speak like a dictionary).
SOURCE
William Zinsser, On Writing Well
