If you asked twenty SEO experts for the best content marketing advice that they could give, what would it be? 
It's easy to summarize many of the responses found in the article from Heidi Cohen on her website.  Be useful.  Useful information will be used and shared.

A number of them stressed the importance of keeping your target customer in mind while creating the content.  This is true of all marketing that you do.  Never lose sight of who the content is for.  Hint, hint, it's not for us, the writers.

Here are some of the pearls of wisdom from the article:
1. “My best piece of content marketing advice is to always be helpful and create marketing that helps people.”  Michael Brenner of SAP and the B2B Insider blog.

2. “Be interesting, valuable, and educational. Too many people write content that is self-serving and uninteresting. People won’t read or share that. Tell personal stories, engage people in a way your competitors aren’t doing, and give away advice.” Gini Dietrich of Arment Dietrich, SpinSucks and co-author of Marketing in the Round.

3. “On the web, you ARE what you publish.” David Meerman Scott author of Real Time Marketing and PR.

4. “Know your audience. If you don’t know your audience, any other rule here won’t apply.” Peter Shankman, Shankman/Honig  and author of Customer Service: New Rules for a Social Media World and Nice Companies Finish First.

There were some other tips included, but creating content that is of use to your target market is a great goal to have each time you sit down to create some content for your website.