The best practice for creating RSS feeds is to make the content of your feed useful and interesting. Ask yourself, would you want to subscribe to this feed if you weren't creating it?
People will be reading your feed outside the context of your Web site, so each item, theoretically, should stand on its own to some extent.
Make It Accurate
Having read RSS feeds for a long time, I know that often, RSS publishers' standards of truth and fact-checking are low. That's one of the main criticisms of the blogging world: While trying to make a point, people sometimes forget about the truth and simply make up statistics and "facts." I've seen opinions in the mainstream press turn from being wildly supportive of blogs to turning away from them on this point alone. I hope the same thing doesn't happen when it comes to RSS feeds.
As you can imagine, if you publish things without checking the facts or providing references, it'll be hard for readers to take you seriously after a while.
Make It Useful
Using Web site statistics, you can determine which of your items people find the most useful. If you want to target what readers like to see, watch the statistics that give you the number of hits for particular RSS items on Web pages.
If something you've written about elicits an avalanche of positive interest, you know you're on the right track.
Make It Interesting
If you want to attract and keep readers, you've got to make your feeds interesting. Too many bloggers feel the need to write something every day, whether or not the content is interesting. So sometimes you end up with blog entries (which go out in RSS feeds) like, "Can't think of anything to say today. Nothing going on. Borrrrring."
And they're right, that's boring. As a publisher who wants to catch readers' interest, you have to look at your feeds from the readers' perspective. If what you have to publish is interesting to them, they'll keep coming back.