I got started by posting drone photos and video on my social media and making it known that I would do this for hire. I took on some one-off jobs that came up through some of my friends, like marketing photos for commercial real estate leasing, some home listings for home realtors (although most of them want you to do the interior photos at the same time), and even photos of a small town for their historical preservation society.
Later, I signed on with Zeitview. They market drone services to clients worldwide and offer the jobs they get to drone pilots who are signed on with them in whatever area the job is in. They are notorious for not paying well, but it's a great way to get some experience in various aspects of drone services while making a few bucks in the process. Think of it as a paid internship. They also provide some online training. I also signed on with Dronegenuity and Fly Guys, who have the same business model. They pay better but don't offer nearly as much work as Zeitview.
There is another type of platform that works more as a middle man just connecting customers to pilots. The one I use is called Droners IO. Clients (the people needing the drone services) sign up with them for free and can post jobs on their site. The pilots who are looking for the jobs also sign up for free and set their location and how far they are willing to travel. Droners notifies pilots of jobs in their area, and they can go bid on the jobs (the client usually includes their "budget", but it's seldom reasonable). Droners has a paid premium feature for pilots that moves them to the top of the list when clients are searching for pilots and also makes it so you (the pilot) can see how much your competitors are bidding on jobs. I recently upgraded to this and find it worth the $29/month. Droners IO makes their money by taking 10% of the pilot's pay from each job.
I am starting to get some regular direct-client work, which pays way better than using those platforms. The upside to the platforms is you can pick and choose which jobs you want to take. With the client jobs, you need to be available when they need you.
As far as marketing myself, I think the next logical step would be to build a website. I also do photography (drone and ground) and sell my photos. Right now, my only expenses (besides the initial purchase of my drones, related peripherals, 3rd party software, power bank for charging batteries in the field, a good laptop for editing and related software) are business liability insurance (a lot of customers require this), my $29 subscription to Droners IO, and the fuel I burn getting to the jobs (I sometimes go out 200 miles or more if the pay is right).
I wouldn't mind spending some money to market myself more, but I'm not sure what would the most cost effective right now. I've also thought about setting up a Facebook business page, but I'm not sure how effective that would be if someone who is not a Facebook user (if they exist!) searches for drone services.
I hope others reply to your post. I'd be curious to hear what they are doing, as well.