Discord, Facebook, online forums, YouTube, itch.io 

This is a philosophical question that has stumped almost all game developers. To me, the question sounds like "How do I get a lot of money?" You just have to keep trying until something works.

On small tip is you can buy ads for specific subreddits that you think might be interested in your game. This allows you to target, say, /r/fishing if your game is about fishing.

Reddit is great for getting game players because it has pages, called subreddits, dedicated to game players.
Colin mentioned buying ads, but you can also do it the manual way. If your not on there already, first spend quality time on there, joining subs you find interesting and posting comments and question posts. Build up karma by posting questions, pictures, devlogs, anything with no links. After you've got around 500 to 1k karma and get the feel of the place, then start to post  link posts, typically you want to only post 1 link post per week.
The main game subs that are for posting links are;  webgames  freegames playmygame  destroymygame  playtesters  webmobilegames. And itch has a sub too.
You can post a link to your game on each one, but you should not post to all of them on the same day.  Wait about three days to a week in between posting the same link to multiple subs, or have different links, like one to newgrounds one to gamejolt one to indiexpo, and wait a day in between posting each link to the subs.
Other subs more for like devlogs are  solodevelopment   gamedev   gamdevscreens.

From what I've personally experienced,  good tagging, naming and labeling does help quite a bit. I've noticed that our games sometimes show up when someone clicks through another game of the same tag, or they pop up when someone filters through tags. There are also some who search through the bar at the top - that one filters in games with matching titles.

Another way is to join game jams. Don't submit games you didn't make for them, though - join them properly. If you can make a good game that's relevant to the theme, there'll likely be a spillover audience looking for more from the same developer who'll visit your profile and play your older games.

Imo the best form of marketing for game devs is our reputation as developers - work of a quality we can be proud of plus content that suits our brand and style.  Even our experiments say things about us sometimes!

I've talked about the fact that I used to be a copywriter in some of my other posts, so I like to think that I know a thing or two about advertising. I have a BIG recommendation for smaller, one-person operations:

You CANNOT go wrong building a community. It's like the best kind of advertisement. Make your project's FB page a source of fun memes featuring your characters, engage in the discussions there, make a Discord, etc. The trick though is that you need to be genuine. It's 2023 and the Internet can smell a suit a mile away (I still smell slightly of mine, I know...). But if you engage in good faith with other creators, try to share your knowledge as much as you soak up from others, and keep a sense of humor about you, you'll have a loyal audience that'll eat up even your worst work.

But it's gotta be YOU. Unless you're a jerk... then consider being someone else.