How can I get better at this? Are there any videos I should watch? Any websites or books I should read? Any tips?
If your site solves a problem, there's probably a lot of forum posts and yahoo answers questions and blog posts about the problem. Google the problem from the user's perspective. For example, something like "how do I make animated gifs from videos?"
I registered an account on about a dozen forums and answered all the similar questions without spammily forcing my solution. Same thing with yahoo answers and blog comments. It doesn't even really matter if you get inbound links or not. With a few days' effort, your site will be mentioned as an answer on all the top search results for the problem.
This seems to me to be the best of the lot; some great descriptive tips and links to other articles.
http://www.wilsonweb.com/articles/checklist.htm
Here's one even mentioning Y-Combinator:
http://www.scribd.com/doc/24126/How-to-market-your-website-o...
And some others:
http://blog.fairsoftware.net/2009/07/09/good-programmers-don...