Try to gain inspiration with things around you and through that think of what mood you want the song to be and find a beat or make one to go along with it. also keep in mind what audience you are trying to reach? what’s your goal when writing the song? what do you want to make people feel? when people listen to your sound is it meant to be sad, excited, etc. you can’t have a moody sad R&B and voice loud and screaming about how happy you are. I hope this helps