One of the easiest ways to get stuck on a project or miss out on sales is to have poor design either by Graphics, Music, Etc. Here is a small compiled lists to make your game look, sound, and feel better which means people will be more willing to check it out & download it.
Please, be very careful that you read and use “Usage rights” found within the art files and even then take your time to read the actual license in the source page.
Game 2D Art – FREE SPRITES, FREE TILESET, FREE GAME GUI, MISCELLANEOUS GAME ASSETS
https://gamesounds.xyz/ – Royalty free music and sounds for your games.