Blowing their own horn. Yes, of course, the primary goal of marketing is to create leads. However, in the age of digital media a brand-centric, salesy approach deflects interest in your company. Make your marketing customer-centric.
Second biggest mistake: Far too often, digital marketers start and stop. You need to contribute a steady flow of content to the channels you use.

Content marketing is the creation and distribution of educational and/or entertaining information assets for the purpose of generating brand awareness, traffic, leads and sales. Marketing content is generally free and does not explicitly promote your brand as an ad would.

A content marketing strategy is a plan for building an audience. Elements of content marketing strategy include establishing objectives, audience personas, a value proposition, content marketing mission statement, a buyer journey map, and plans for creating, promoting and analyzing how content marketing assets and programs perform.

Email, social media, search and other elements of your digital marketing mix will depend on delivering useful content. Though video outlets, podcasts, and media galleries present other options, a blog is by far the most used tactic for distributing marketing content on a channel over which you have complete control.

There can be no all-encompassing answer to this question except to say you should create content buyers will find relevant and useful. Leading candidates include blog posts, articles, ebooks, infographics, microsites, videos, courses, case studies, newsletters, visuals and various forms of interactive content.