Email Marketing has become very straighforward for small business these days thanks to the many tools now available. Thanks to companys like I-Contact and I-Robot, small companies can do regular email campaigns without much time and energy. So, then you need to ask yourself... If it's that easy, why am I not doing email marketing already?
Because you don't want your newsletter viewed as Spam, getting customers to opt in is the best way to build a relationship over email. The other benefit to using a service, is generally the emails automatically include the Opt-Out function, which is a neccesary evil these days because of the CAN-SPAM Act. Which every small business should be aware if you are doing any kind of emails to your customer base.
One concern people have about emailing, is the concern that it will be viewed as Spam. If you haven't ever emailed your customers, then suddenly you are emailing them every week - they are likely to opt-out. It's important to set expectations of the "email relationship" as you begin in with your customer. Tell them on the sign up page how often you will email them. And the most important, stick to it!
The last and most important thing about your email is give it some value. Make sure to always include something for the person who is taking the time to open it up. It could be a discount, coupon code and free gift with purchase. But don't fall into the trap where you are concerned that too many people might redeem your offer - you should be so lucky. It will take a long time to even train your email list about the cool things you have to offer. Unless your email list is thousands of people, then you don't need to worry about this early in the process. But you need to offer them value often and keep it exciting! Of course, the branding opportunity and positioning of your website is also important when doing your email marketing. So, use good graphics and strong copy. But remember, even the prettiest email is useless if it has no value to your customer.