How to find content ideas that sell

TL;DR:

Identify the customers you like (who value & support your business) and why you like them.
Examine the perception your customers have of you, based on what and who they would consider an alternative to your product or service.
Compare the features and capabilities you have that competitors don’t, to discover why your favourite customers pay for you.
Match your unique features to your customer’s ultimate goal, and the task that your feature helps them solve.
Identify your best-fit customers, who are interested in the outcomes your unique features deliver, so you can optimise your SEO and content marketing activities.
Identify the specific pain points that bring customers to buy your products. Look for questions that potential customers may ask online. Social networks, communities, niche websites, and competitors are all sources of information.
Merge and use all elements:

Alternatives: analyse competitors and their properties
Unique features: uncover different ways they are defined, find related topics, utilise language customers used during your interviews.
Goals & Tasks: Analyse forums, Facebook groups, Q&A websites and Reddit to expand your keyword research and find new competitors.
Audience: create content for your ‘best-fit’ prospect customers, who are more willing to buy from you than anyone else.