No matter how far society can advance into the future with technology, shit and water will always need to run downhill and have clean pipes to do it. Guess what- 21st, 22 or 29th century folk still are still gonna need pipes to get water. Know that.
If you've got any kinda skill like plumbing, handyman stuff, computer repair etc, post flyers with your phone number on small tabs folks can pull off and take with them.
Suggest near markets for housewives to see for handyman stuff; near college housing, dormitories, and on campus bulletin boards for computer tech stuff.
Most churches have bulletin boards. Pay attention to what others are charging for services and beat their prices. Everyone needs drains cleared out. You might find out what it costs to rent a drain snake and maybe just charge a bit more. I don't think you need a license to clear a drain or change a drain pipe. It's not rocket science.
It won't be too hard to undersell pro-drain cleaners. No experience? Ask a friend who does to show you how. The thing is getting your flyers on every church bulletin board, college dorm bulletin board, or college bookstore etc. Most kids in college can barely tie their shoelaces beyond buying fast food. If you plumbing like replacing a drain pipe, (always) check your work by running water in case you need to tighten a joint more. Light electrical work like replacing a fixture or even painting- some folks are completely helpless at.
For repairs, tell people you will need include what it will cost for parts, then add your fee.