Richard Hoy at Writers Weekly provides some generous advice on marketing online: I think that this is good for those of you who have a website and would like to get it more attention. However, unless you're Nick Denton, you need to build a web presence, so don't think to yourself, "If I make a website and follow these rules, I'll have clients beating down the door!"
There are really three "core truths" about marketing on the Internet.
1.) The Internet is basically a collection of niches. Just about any subject you can think of has a group of followers. Identifying where those followers hang out online is the first step in any online marketing campaign.
2.) Be a good, honest source of information for the audience you are trying to attract. That garners people's respect online. You should not give a slick sales pitch about how great you and your product/service are. People hate that. And it is dishonest because nobody can guarantee to solve everyone's problems.
3.) Never force yourself on anyone. Treat all interaction just like if you were meeting someone in the real world. You wouldn't start randomly pulling strangers off the street and pitching yourself to them, would you? Likewise, you shouldn't do that online either.
More here.