Once you establish yourself as an authority in that field, or at least someone who can reliably provide useful advice, selling your product becomes significantly easier. In some cases, people will even want to give you money just to support what you do.
If you sell a product or service for, say, wedding photographers, create a blog that covers topics relevant and radically useful to this particular niche of photographers. Perhaps make a YouTube channel on the topic, hang out in the forums and groups where wedding photographers are, leverage social media, etc.
Find out what they need and satisfy that need, not just with your product but with your content as well.
And how do you aggregate/consolidate your efforts through various channels? Mailing list. Nothing beats email.
Make sure you collect emails from day one and keep your list warm by providing great content regularly to those who subscribe.
Occasionally, you'll drop in a soft sale and special discounts for your loyal subscribers. You'll be surprised at how many will buy from you because they know who you are and trust you on the subject manner.
There are of course paid strategies if you have the budget, but I would first focus on organic audience building.
Best of luck.
https://news.ycombinator.com/item?id=15002079 (Aug 2017, 68 comments)
https://news.ycombinator.com/item?id=14942902 (Aug 2017, 68 comments)
A list I compiled of 4 HN user authored books on marketing and their launch discussions:
Most important, I don't know, how long will it continue. So sad.