That's an often asked question. Look here and here for example, just on the first page of this category. It's hard to give more specific advice without knowing details. What game is that, and what did you try? How are your other games doing?
My game is an android space shooter controlled my accelerator, currently working on multiplayer mode. I tried posting it in advertising channel on some discord servers, my other games doing better, 200-500 imressions and 2-4% CTR, thisgame have 0 impressions.
