I made a rookie mistake. Normally I take quite a bit of time to ruminate on a name before I create a character. Normally....
But I named two characters on the same server both with names that start with the letter "J." That doesn't seem like a big problem except the fact that I mail things to myself all the time. Herbs to the alchemist... items to be enchanted... food from the cook... armor kits from the leather worker... etc. And by naming two "J" characters I broke my general naming rules and my normally orderly mailing (read: autopilot) has now turned to chaos (read: no idea where I just sent that).
Here are some of my general naming conventions:
Name to take advantage of Autofill - Unique first letters
Step 1 - Put the names of my alts in each of the others friends-list.
Step 2 - When I mail something to an alt, type just the first letter and the mail system autofills from the names of people in your friends list.
And as I learned after the great Friends-List-Wipe of 2006, if there's no one in your friends list it autofills with the names of the people in your guild (which for me is filled with alts who haven't logged in since the great There's-Not-Enough-60's-In-This-Guild-To-Raid-With main-character-migration of 2005). It took a month for all that stuff to get kicked back to me.
Autofill, my one time friend, turned into my new problem with the two J characters. I would enter the letter J, for "Jill" for example, but instead it autofills "Jack" because his name sorts first. Oops, wrong mail. Again. At least this time its still to me, so it only takes two hours to fix.
Name to take advantage of Autofill - Avoid certain letters
I also try not to have names that begin with "W" or "B." Why? Because I can't tell you how many times I am in the middle of sending a piece of mail but change my mind. I then try to walk away and press "W" or try to open or close my bags and press "B." Instead of closing the Send Mail window, I wind up filling in the name of someone on my friends list. ("Briar" actually gets a lot of errant mail that way.)
To show you how truly lazy I am, my new rule is to pick names of characters whose letters are around the WASD keyboard position. E, C, V, R, T, G, B, F ... all good choices. This way my left hand barely moves. You think I'm kidding; I'm not. Someone can actually BE this lazy.
Although I tell myself it's "efficient."
Anticipate future name variations - Titles
This isn't really a problem for me because I don't engage in PVP. But I still try to anticipate what a name will look like with a title in front of it. The name "Rume" may sound fine on its own but rank up to "Private Rume" and expect some weird whispers.
Compare to Other Character Names
When you're naming you may benefit from reviewing Naming Patterns courtesy of PlayOn (Exploring the social dimensions of virtual worlds). It's a very interesting read. Also check out the link I mentioned previously that can show you existing player names across servers.
Update 8/2/2007: Mark of the Wild's Naming discussion with good comments.