Doctor, this may sound silly, but how do you sound to yourself in the shower? It happens to be a great place to practice singing. First, there's no one there (usually!) to make faces when you hit a wrong note. Second, the White Noise background of a shower can let you concentrate on your voice.Something to remember is that it's difficult to sing along with someone who's not in your own range. If you're a baritone, find a baritone to sing along with, not a tenor, and you'd probably do better singing the lower line with women in the alto range than with sopranos. If you're a tenor or bass, then you're probably going to find it easier to hit the notes singing along with a tenor or bass or soprano. Straining to hit a note above or below your abilities doesn't help.
But most of all, remember that the injunction is to make a joyful noise: Nowhere does it say you have to be able to carry a tune or stay on key.
Sarah