First, learn how *not* to be a jerk

It's really embarassing to get reported for spam, and blacklisted. Here are tips on how to properly manage your email lists and follow best practices...

I recommend: Start off with MAPS. They're a major blacklisting service, and they've posted some guidelines on how to properly manage your email lists.
You don't ever want to get on SpamCop's blacklist. Here are their tips on how legit marketers can avoid getting blacklisted.
No email marketer should click the send button without reading through the FTC's CAN-SPAM laws.
 Read through the ESPC's email marketing best practices guide (PDF download).

Learn how to design and code HTML emails

Even if you use a tool that designs your emails for you, it helps to understand how everything works behind the scenes.

I recommend: Read through some HTML design and coding resources, like: MailChimp's free email design guide, MailChimp's free HTML email templates, Tim Slavin's "How To Code HTML Email Newsletters"

Learn how to measure results and optimize

After you get used to sending email campaigns, you'll want to measure clicks and opens, and start testing different tactics to improve your ROI.

I recommend: Bookmark these websites and subscribe to their
email newsletters: MarketingSherpa, Mark Brownlow's email-marketing-reports, MailChimp's MonkeyBrains Blog, ReturnPath's Resource center, MailChimp's "Understanding Email Campaign Reports" and ClickZ's email marketing resources

Deal with inevitable deliverability problems

Sooner or later, you're going to notice a bunch of your emails just aren't making it into the inbox. Evil spammers are making it worse for the rest of us legitimate marketers.

I recommend: Download this very excellent overview on deliverability from the IAB, read MailChimp's "How Spam Filters Think"