As I've mentioned before, and will mention again, freelancing is a business. Business requires customers, and freelancers who create content (writers, course developers, etc.) essentially have two types of customers: people who pay them to create, and people who read or use what's created. Sometimes both types are in the same entity, such as a company that hires you to create a course for their own people to use in-house around some of their own tasks. Many times both types are separate entities, such as writing an article for a magazine, which is then read by the people who subscribe to that magazine.
As a business, you obviously need to cultivate both groups, yet in a way you can do both at the same time. The key is to always remember that you're promoting your business, and so don't break down into someone who spams everyone they know every time they do some little thing. At best people's eyes will start to glaze over and they'll miss the interesting stuff. At worst, all of your email to these people will end up being filtered automatically into the Delete box without a glance.
I find it helps to have a routine. When I get the word that an article of mine is up, I first post about it on my blog (this lovely place you're reading now). I make sure to include a link and a summary so people can tell if it interests them. On the upper right of the blog you'll see a spot where people can subscribe to my mailing list. Subscribers get an email each time I post to my blog, so again, that's an incentive to not post about every little silly thing or they'll either leave or just stop paying attention. The lower left has a list of the various news feeds my blog supports, allowing those who don't want emails flooding their inbox to be notified through RSS or whatever method floats their proverbial boat.
After placing the information on my blog, I also post a shorter mention on Twitter, which I suppose you could call a micro-blogging site. I may or may not mention it on Facebook, as I've registered my blog through the blog network application, which will allow people to follow it automatically. The bonus of doing things in the open such as through your own blog and sites like Twitter and Facebook, rather than just sending out email announcements, is that people can find your work just randomly by stumbling over it, or through Web searches, or through recommendations from other people who've found you through various random means. Part of promotion is creating opportunity. Make it easy for your work to be found. Some of the people who find you through Web searches or through seeing who their friends are watching will be editors and others looking for freelancers.
Not that all of your work will end up online. Those are just the easiest items to share. If most of your work ends up in private hands or is otherwise not something you can post pointers to, consider other methods of promotion. There are a lot of professional organizations, for example, who can use speakers. While the idea of public speaking might make you feel a little woozy, doing talks is a great way not only to make people aware of you and what you do, but also to give back to the community, and to add to your promotional reach by the simple fact that the organization will also promote your talk as a way to get members to come in and listen. Starting with small groups and working your way up to larger ones is a great way to get used to public speaking, and can even broaden your resume into offering workshops and classes once you're comfortable.
Building promotion into your regular routines is a great way to make sure that you keep the business side movingas a side effect of completing work and sending out invoices. You'll still have to spend additional time on market research and hunting down potential new clients, but in the meantime, you never know, some of them may just find you first.