I agree with Jerrie. A popular way to get work is from freelancing sites. However, these can be competitive so you may have to lower your price and will need to find a unique angle to stand out from the mass amount of developers these sites attract. Maybe you have specific insights to a certain niche or solve a very particular problem that others face.
That may be your best option to start out, this way you can build up a reputation, get reviews, and start a portfolio. Another way to start out, is to hit up business contacts, friends/family, and your existing network. Those are pretty much your 2 main options.
Then, ideally, you’ll want to be getting clients yourself. This way you would be able to charge your full rate and establish long-term business relationships. This is where having your own website, being active on social media, maintaining a blog, sending out emails, creating ads, etc… all come into play.
There’s a lot that goes into something like this, so I would start now by researching what’s in demand in the marketplace and how your skills can benefit people/businesses. I would also come up with a brief business plan (maybe a few pages, at most) which explains what you’re going to do, how you’re going to do it, who is your target market, your goals, expectations, pricing, marketing, etc…Just helps to have stuff written down and use as a reference.