"Growth Hacking" relates to identifying highly efficient ways of growing business.
Where efficient, to me, tends to by $0 methods, as these scale forever.
If you can create a $0 based system to grow your revenues, you can plow huge chunks of cash for even faster profit increases.
I tend to use this approach to validate ideas + just to bring in new waves of customers/clients.
My approach is Meetup trolling.
Attend Meetups where people will be who can use your product/service/information/courseware + where you have zero competition.
For example, one of my companies provides high traffic hosting for WordPress sites.
Easy places to pickup new clients/customers include any Meetup.com group event where people network... because... likely many have WordPress sites + most hosting tends toward slow + glitchy.
Likely no one else will be pitching WordPress hosting, so I'd have no competition.
This example is using offline tech to push to online service.
You can use the exact same approach to promote lawn mowing, only you call it... Executive Landscaping...
Or coaching or computer repair.
Marketing is marketing. Whether your product is online or offline.