In my hands is a State Of Marketing report that says the top marketing priority of pretty much every type of business is to get a grip on content marketing.
So here's the key rule for content: It's got to be informative, engaging, and/or amusing
Content is used in:
* website design
* SEO (search engine optimisation)
* social media
* pay per click advertising
* email marketing
So basically, put every piece of marketing collateral through the informative/engaging/amusing filter first, to make sure it's at least one of those, but then see if you can make it better in those areas.