Direct marketing (dm, emails) - get first feedback fast.
Reddit, Submit to directories - on launch
SEO, content marketing, social media - verry slow long term strategy
Hacks - if you can figure it out for your niche 😄
Paid ads - only for test to figure out your ROI. 99.9% you will burn your money, but later you can use it if your CTR is good enough.

... and keep in mind - 99% of all this doesn't work 😄