Don't use more than three typefaces. Follow a grid. Keep it simple.
But adhering to the rules doesn't always leave room for creative inspiration. As David Ogilvy said, "Talent, I believe, is most likely to be found among nonconformists, dissenters, and rebels."
In marketing and advertising, we value those who are willing to challenge the norm and question the how -- the creatives who discover a novel solution by ignoring the brief and looking at the problem in a completely new way.
But you can only break the rules if you know the rules.
DesignMantic created the below SlideShare outlining the typical rules followed in design and why you should consider breaking them this year. Check it out to learn how exactly you can become a more rebellious designer.