Mainly just get your product or service in front of yoru target market, think about where they chill at online and get in front of them.
First find an audience. Where do they hang out? Then, build a list by providing them value for free. After you have built trust, then promoting your product will be much easier.
There are various ways that you can consider for general marketing of a product. These are, among others, Social Marketing, augmented marketing, Direct Marketing and online marketing.
What product are you thinking about? Is it informational product, physical product? Your tactics could be different depending of niche and type of your offer. I know people like free stuff (Gifts, quizzes, coupons) - that could be something to get them into the door and get first sales.