A lot of this may be common sense but i'm going over my knowledge of ways to keep you account and game e-mail safe!
E-Mail:
First and for most, make a completely new e-mail just for your WoW account! Since all accounts are battle.net now it is required to use the email for everything. Make sure it is a different password from you're WoW account and other e-mails too. Make sure the name is unique.
Here are my favorite E-Mail Provider's.
Yahoo
G-mail
Doing this will keep your e-mail for your account private. Never use this e-mail to sign up anywhere and don't post it anywhere. By doing that you prevent yourself from being e-mail phised. I can not 100% guarantee that NOBODY will ever find it but it's a very slim chance.
Account:
Let's start off with common sense, don't tell ANYBODY you're account information unless they are blood related so you can punch them.
Do not click on any link people send you in game saying your a lucky player and to sign in on some website to retrieve a prize or anything of that sort they just want your account.
Never click on links that are from "blizzard" unless you can tell the website is spelt correctly, sometimes they use the number 1 in place of an l. If the site is telling you to enter your account information DO NOT do it. First log into your WoW account at battle.net and see if anything is up. If nothing is wrong then the e-mail is obviously fake. If you are still concerned you can always call Blizzard's hotline.
Do not under any circumstances lend your account to chinese farmers for renting, they WILL get you banned sooner or later. Same goes for buying/selling gold, botting, and power leveling.
If you are trying to sell your account do it legit never trade or sell to somebody that has a bad reputation or none at all. Always do background checks on markeedragon that place is loaded with scamming scum who will not hesitate in stealing your precious account and/or money.
FOR THE ULTIMATE HACKER DEFENSE!
Get a authenticator, plain and simple. These babies attach to your world of warcraft account and give you the extra security to ensure you will never be hacked by somebody unless they rip that damn thing out of your hand and figure out your password too.
How the authenticators work!
I'm not gonna try to confuse it so i'll put this simple but thoroughly explain at the same time. You're authenticator has a unique code that you use to attach it to your account. Once it is attached every time you attempt to log into WoW or account management it will prompt you to enter the randomly generated code the authenticator produces. Once you enter the code you gain access to your characters, management page, etc. No code is EVER the same it is completely randomly generated.
"So hey trojan if i get this authenticator couldn't somebody just use their authenticator code on mine?!"
Wrong! Remember that unique code that linked your authenticator to you're account? Well that little code makes your account only work with codes generated from the device with that matching code!
You can either download the BLizzard Authenticator App from iTunes if you have a iPhone or Buy an Authenticator from Blizzard!
(Other phones are capable of using the authenticator as-well but i won't be covering that)
Itunes Link
Blizzard Store