1. The native ad should so closely match the natural user experience that it should feel like it is a feature born out of the site, not something that was ad-served on top after the page loaded. As native as Facebook's ads, Promoted Tweets, LinkedIn Sponsored Updates, and Promoted Pins, native ads should feel as if they emerge from the fabric of the site, not ads overlaid on top that look like they were added as an afterthought.
2. Native ads should match the “atomic unit” of the site. Often there are different atomic units to choose from, but rarely should a native ad be designed as something entirely different than the natural atomic unit of content for the site.
3. Think as if you were the product/UX lead building a core site feature. Sometimes a site's natural story units (atomic units) will not have all of the necessary components for a fully formed native ad. When adding new components that may not be part of the "atomic unit" of a normal story, we should think as if we were the developer/UX person at the site, and design features into our ads in a way such that those features could reasonably end up being features of the normal story units too.
4. Always try to be in a feed. Whether that's homepage or channel feeds, or feeds below the post on article pages.
5. Mimic the richest item in the feed, not the sparsest.