1. Find a Subject You Care About
2. Do Not Ramble, Though
3. Keep It Simple
4. Have the Guts to Cut
5. Sound like Yourself
6. Say What You Mean to Say
7. Pity the Readers
8. For Really Detailed Advice...
Read this post by Maria Popova, my favourite blogger, to understand what Vonnegut means: "How to Write with Style: Kurt Vonnegut’s 8 Keys to the Power of the Written Word".