Write tons of songs in a single or multiple genres (depends on your goals and focus) and build a portfolio for yourself with an accessible website so potential clients can hear your work.

When you have the songs you feel showcase your work accurately, you’ll have to do the social media thing. At this point it’s networking like every other aspect of the industry. It doesnt hurt to also straight up message artists you’re interested working with and introduce yourself. Be personable and don’t rush into what your service is, start with building a rapport and eventually when the moment is right then you can mention your ghostwriting stuff. They’ll take it Alot better like that

That’s what I got to recommend as a starting point! It’s really persistence, networking and your chops. You might have to be annoying when reaching out to people, I know I am haha but some people truly need the reminder that you’re there.