Copyblogger has just released a post entitled "Copywriting 101: An Introduction to Copywriting". It's a hands-on, practical list of things that you should do when writing copy (content) for online media.
We would also add an eleventh point to this list: Do NOT forget about your instructional content. This includes content on your forms, error screens, pop-ups (if you have them, which we don't recommend unless there's a really valid business reason), checkout processes, and other "hidden" areas of your site. Most of these screens are presented to users during key conversion steps--i.e. right before they're about to buy, enter a credit card, join your mailing list or otherwise convert. We've seen many, many web site owners neglect these areas, and then ask why they're not getting good results. All content on your site, including instructional content, should follow the steps outlined in Copyblogger's Copywriting 101 post.
Speaking of results, we urge all of our clients (and you) to leverage web analytics tools whenever possible to identify areas in your copy that need help. Many analytics products, such as the ultra-impressive ClickTracks Analytics by Lyris, will even analyze your content for you to tell you if it contains the right keywords, which keywords are performing the best, what keywords other web sites are using, and lots of other valuable information.
Interested to hear your thoughts on copywriting or analytics...