I just dove in this world and launched an app that I myself used in my other business, so I thought if I am ready to pay for this then probably there is more people like me. I didn't know how SaaS marketing worked but I just started researching, one thing I knew for sure in my small local business is that nothing beats paid advertising so I did just that with my app.
In the end I think the advertising knowledge from my small business and the idea that "what I would pay for other people would also pay for" were 2 main things that made me have success in my first launch.
Just to be clear what I call "success", in two weeks I have 30+ signups and already a paying customer when I didn't expect even 1 signup, I don't have a big following in any social media, so it's not earth shattering but for me it's success.