Looks like the cat’s outta the bag regarding what Google looks for to rate a website for quality. Most of it is common sense, but it’s encouraging to see that quality is rewarded a better rating. For example, citing your sources strongly indicates trustworthiness.
The nice people at AudienceBloom made this colorful infographic from Google’s leaked quality guidelines containing good practices for your website’s content. This can give more weight to webpages’ messages and help serve your visitors better. Check it out.