eMail Advice and etiquitte that I have found helps

I am not going to claim that I am good at writing emails. In fact, despite writing several books, hundreds of published articles on all sorts of topics and literally 10's of thousands of emails, despite being one of the first people in the world to use eMails (I started using email heavily in 1980 - and YES some people had used it for YEARS before me), I still don't do eMailing completely effectively.
However, I have learned a bunch of things that DO work. I have learned much from my mistakes.
And so I offering to share some tips for your consideration.

Subjects:

The first tip is - Make the subject line USEFUL! Not "Hey" or "as you requested" etc.., Take 3 or so seconds and think up a subject line that will identify to the reader a month later what that email was all about.
If you are replying to an email because that is the PERSON you want to talk to, but you are talking about a new topic - take the few seconds and change the subject line. It is very rude to reply to an email and not change the subject line - when you changed the subject!
Here is an old trick not practicsed much these days. I learned this one from Bill Gates back when he was running a little company named Microsoft and I was beta testing his wildly successful MS-Pascal. (OK, so the product didn't work out all that well, but really - I did learn this trick from Bill back then)... Put a tilde ~ at the end of the subject line when the subject line says all there is to say. That way the user knows they don't need to open the body of the email to read anything more.
If you have 2 or more different topics - give serious consideration to sending 2 different emails each with a good subject.
Duplicate the Subject line in the Body. There are some people I have met that never (or sometimes don't) read the Subject line. And I've had some REALLY big blunders when people didn't read the subject line and then got the completely wrong idea by just reading the body.
Use upper AND lower case letters in the subject line.

Attachments:

Check the size of your attachments. Most people can't accept anything bigger than 5MB - and many people can't accept even that. Ask permission before sending large attachments.
Make sure your attachments are virus free before you send them. If you don't know how - don't send it!

BCC: Blind Carbon Copy

When sending an email to people that don't know each other well - use the BCC, don't use the TO: line or the CC: line. If you don't know what the BCC: is - find out - it isn't difficult! If you use Outlook, search the help for BCC, it will give you step by step procedures to set your email up to always have the BCC available. When you put a bunch of people in the BCC, each will get a copy of the email, but they won't know who else you sent it to. If I had my way, the BCC would be the FIRST option available. There are lots of times that I see that someone sent 100 people an email and I can see all 100 - and they can see mine, and I don't want that. I get enough junk email as it is.

Body:

All CAP's mean that you are "yelling". All Bold means that you are saying "Pay attention". If you do too much of it you are saying "Hey STUPID - pay attention".
It is OK to CAPITALIZE individual words to emphasize those words. Think about when you speak - if you would say a word louder than the rest in the sentence to make it clear to the listener what you are saying - considering bolding, capitalizing and/or itallicining that word in your writing. Consider: "I am NOT saying you should put lots of words in capitals." I frequently capitalize the word NOT because too many times people have read sentences and they miss the word NOT - and wow, what mistakes THAT makes.
Use emoticons. Like :-) or <g> or <rofl> to let the reader know your EMOTION while you are writing. Elsewhere (in the fun and educational) you can read my section titled "English Progress" for a more detailed (and fun) discussion on this and how you can make yourself better understood.
Duplicate the Subject line in the Body. There are some people I have met that never (or sometimes don't) read the Subject line. And I've had some REALLY big blunders when people didn't read the subject line and then got the completely wrong idea by just reading the body. (btw ... there is a joke in the fact that I duplicated this tip. Hope you caught it before you read this sentence!)

Signatures:

Now if you read this and say "but I CAN'T put my signature in" then you are the person I am talking to! On every email package I have seen and used in the past 27 years, there is a special feature called a "signature'. This is what will be tagged on to the end of every message you send - and they usually have an option for it to be tagged on to every reply as well. I recommend that you include the following info in your signature:

A polite ending. Something like "Regards". In my case, because I deal with Spanish and Chinese a lot, I include the Chinese and Spanish "thank you' as part of this.
Your Name. When someone is whipping through a bunch of emails, seeing the person's name (as opposed to their email address) can often make it easier for them.
Your phone number and fax number if you have one. If the reader reads your email and decides they should call you on the phone - why make them have to go and look it up? Why not make it ALWAYS there for them.
Your mailing address. Same reason as for the phone number.

Some people like to add something that is representative of them. It may be something about their business, it may be something about their favorite hobby, it may be something about the environment, it may be a pet peeve or today's hobby horse. If it is more than one line long, I like to only use them when they are on a "new" subject, not when replying, I usually prefer to leave the shorter version for replies.
Some companies require that you include a disclaimer and warning that if the email went to the wrong person it should be deleted. Not that that is likely to happen, but I assume they do it to try to protect their legal position.

Some emails just should never be sent...

Don't ever send greeting cards etc.., without asking permission of the recipient first. Why? Because some of those companies use YOU to give THEM your friends emails so they can then sell them on email lists that will then send millions of junk emails to your friends. How to win Enemies and lose friends - send them a greeting card that then doubles their junk mail.
Ask permission before passing on chain eMails, cute emails, "inspirational" emails that threaten the user at the end - you know the type, they have a really good message and then say you are a bad person or something bad will happen to you if you don't pass it on to at least x people. The people who create these think it is funny when you waste peoples time by passing them on. And you can be SURE that if a message ends with "if you don't pass this on you have no heart" there will be a lot of people who when they read that will lose all the value that they MIGHT have gotten from the supposedly educational or inspirational stuff above. My experience is that, when I find crap messages like that at the end, if I then go back through the supposedly good text above, I start to find subtle flaws (especially in the ones that portent to be Bible based - any that have threats or "good luck if" messages at the end are clealy NOT Bible based.They are crap.)
Ask permission bedfore passing on emails that give a warning about some virus etc.., I have received 100's of these emails through the years and you know what? EVERY SINGLE ONE - NO EXCEPTIONS (As of June 2008) has been a FRAUD designed to waste peoples time. Do NOT send these on. And if you MUST send them on - do NOT send them to me.
Do not send on any emails that say "If you pass this on Microsoft will pay you $x for every user that..." These are just STUPID pranks designed years ago..