Sample partial feed: Ars Technica <http://feeds.arstechnica.com/arstechnica/index/>

Content

Provide sufficient content to give for readers who will have to decide whether to click through to your site to read the full story (at least 2 to 4 paragraphs of text)

Showing the number of remaining paragraphs is also a good indication for readers.

Images

Good visuals that support your stormy make for a nicer reading experience in feedly, including for partial feeds.

Be sure to use high resolution images

Mobile Website

Have a website that is optimized for mobile