E-mail is still the biggest online converter of sales, so a list is essential.
These are the top tips I've found around getting sign ups:
Put a sign-up form on your website (the footer is good because it's on every page) with a REALLY good deal for signing up, not the usual 5% or 10% off one order.
Setup an auto-responder to issue the voucher/deal and welcome them to the list.
Send out an email at least once a week to keep the list alive and keep in touch with your customers.
Don't always sell, just send news and a hello, how are you.
Matt McGarry is a great resource to follow to build an email list, i.e. group of people ready to buy your products. He's on YouTube and Twitter.