One of the issues with many content marketing strategies is that while they state very specific objectives, none of them defines success clearly.
The first step in addressing this issue is to look at the goals of the campaign. Clearly defined goals make it easier to define targets and see the outcome as positive. Here a few goals and things to take into account when defining success:
Is the organization looking for more leads? A goal like this needs specific definitions in order to measure success. Firstly, a proper definition of what constitutes a lead. Then what increase on current levels is required to consider the strategy a success. This will have no bearing on converting those leads to sales.
Do the social media networks need more followers? Even a metric like followers will need specific figures for each social media network. In addition, define the increase as a numeric figure rather than a percentage.
How about an increase in sales? Measure this alone or in tandem with another goal like lead generation. For example, an increase in leads without a corresponding lead in sales will highlight problems with conversion.
Always look at available analytics to establish baselines. We need to know what works and what does not to make sure that time is not wasted pushing metrics that are not productive for sales of our products.