You already have a business, so some of this won't apply to you, but you may find useful techniques for marketing your business in our own Jennifer Laycock's free ebook: Zero Dollars, a Little Talent and Thirty Days
. And, of course, there are plenty of ideas for online marketing in threads on this forum. We have a number of discussion areas
related to all aspects of online marketing. You can probably spend several days just reading through what's already been posted.
For more in depth help, you might want to check out Jenn's ebook Small Business Guide to Search Engine Marketing
. It's not free, but it will lead you through all the stuff you need to know to get started.