I've launched multiple side projects since the early 1970s. Nothing in the way of marketing has worked for me, but I think I have finally found an approach that works.
I know it's counter-intuitive, but, trying to find customers is actually a mistake! It's too much work for too little return.
The right approach is to devise a method to find someone who will find customers for you. This might be deeper than it first appears. Consider this example.
My current budding project (call it E) is a tool for students who are having academic problems. Before, I would have tried to convince students that E would help them. Instead, my current approach is to find people whose problem is not to improve their own academic work but to improve the work of others. My value proposition is directed at them not at students. It is their problem I am trying to solve. E solves their problem by giving them something they can offer to students needing help.
Now my effort is to approach academic advisors, tutors, remedial educators, learning disability psychologists, and the like via professional associations and activities. In a sense, these people have become my market NOT the students. They will work for years for free and share their success stories to fellow workers. This sustained compounding effort is the sort that can lead to exponential growth.
Devising a method to find such people can be difficult. Deep thought is needed.
Who really are your customers?