[Mathnerd314]

Easiest (lowest risk) method AFAICT is consulting. Make a webpage, do some SEO & a few keynote talks at big conferences. Once the consulting is paying well, quit your (presumably proprietary) job & only accept projects that involve free software. See e.g. https://blogs.gnome.org/bolsh/2009/02/01/free-software-consu..., there are tons of wordpress shops for example.

Another method is to get skilled in another profession, e.g. law degree, accountant, chiropractor, etc., work in that for a while, build up some custom OSS software to use in that work, promote it & get a userbase, then quit the main job and sell software support / premium addons.

Final method is crowdfunding, for example see https://en.wikipedia.org/wiki/Diaspora_(social_network) as a free software version of Twitter/Facebook, although I think crowdfunding has gotten harder since then so now you need an MVP or something to succeed. It's great for consumer software, particularly for moving codebases from beta-quality to production-ready.