I found this worthy of copying because it's such a concise guide. I've emphasized my faves. I've waded through my own share of unintelligible subject lines in my nearly twenty years online. Holy shite! Has it really been that long? Uh, maybe only nineteen? From AmericaBlog:

John's Top Tips for Insuring Your Email Does NOT Get Read

1. Don't include any subject line at all - that ALWAYS gets my attention.
2. Make the subject something catchy, like: "Read this"
3. Just send me a URL with nothing else in the content of the message.
4. Send me some article, from God knows where, and don't include the URL of the article so I can link to it, or even confirm if it's for real.
5. Send me WORD documents as attachments, I never read those because of viruses.
6. Tell me to post an article that's already on the blog.
7. Ramble for a long time and don't get to the point until, oh, the 7th paragraph.
8. Ask me a question that you could answer quite easily with Google. [Or by actually reading what I've written on the subject. Do you have ADD or what? Oh wait, that's me...]
9. Send me an email about a typo I've made (which is fine) and then get really bitchy and holier-than-thou about it (not so fine).
10. Complain incessantly about me not posting some article or link you've sent as if I'm doing it on person just to spite you.
11. Don't update the clock on your computer so your email automatically flies to the bottom of the heap since my computer thinks it's hours old.
12. Send me that email about "Dear Dr. Laura" that quotes Leviticus and talks about selling Mexicans as slaves. That's as funny now as it was FOUR YEARS AGO WHEN IT WAS WRITTEN.