Programming

I used google ads with very specific phrases and geolocation limited to rich countries. I spent a lot on it, the sales were like twice of what I spent, but I got some good contacts from it and they kept coming back for more.

But, and that's a big "but", I was employed before, noticed a niche that no commercial provider filled, and created my product. It wasn't an idea that I thought was fun or could change the world.

Not gonna lie: my first customer was a place I interned at when I was a student. So I knew who to contact, and what the potential value of my product was, as it was tailor made.

After that I started with contacting other companies via linkedin. Here my "trick" is to contact managers with an engineering background, as they more than often speak my language. In other words: I look for people who (a) have a technical understanding of their production process and (b) are high up enough on the corporate ladder to have a say about spending. Weirdly enough: a rare combination.