Firstly, making an excellent game is a solid marketing foundation in itself.
Then, post to reddit communities that involve your game's genre. ie, turn base tactics, cRPGs, etc. Preferably post during development if you have something to show.
Same with discord.
Both reach potential players directly.
As you get closer to release, with cool stuff to show, contact regular gaming media with your pitch. Hopefully some of them cover you game.
These are what worked for me.