My personal favorite approach is to start by identifying the pain points of your target customers that your product/service is focused on solving, creating informative content aimed at solving their problems, and promote that content to the right audience.
Customer interviews are a great starting point for identifying the pain points of your customers. From there, look towards guys like Brian Dean (backlinko.com) and Noah Kagan (Sumome.com) for inspiration on what incredible content looks like.
Regarding content promotion, Facebook Ads can be a great starting point. For those on a budget, I've developed a content promotion technique that has driven incredible results for some of our clients called the Twitter Leapfrog Method (you can read all about how to use this system here: http://junto.digital/blog/twitter-leapfrog-method-simplified-content-promotion/).
Create a mailing list signup form and other lead capture tools like ebooks to make it easy for your customers to stay in contact with you, and leverage email marketing to nurture those leads with additional informative content.
Low average order value products/services may be simply able to stop here, while higher average order value products/services may require sales outreach.