Most people are good at singing some Kareoke music… you just have to find the right artist that fits your voice. Everyone’s voice has different qualities and if you try to be (or sing) something that isn’t you your singing will suffer.
Over many years of singing in my car and singing kareoke songs in bars I have learned that I can really rock Bob Dylan. So I mostly sing stuff such as Like a Rolling Stone, Knocking on Heaven’s Door, Rainy Day Woman, Positively 4th Street and other hits like that.
On the other hand, when I have tried stuff from Tom Petty, Led Zeppelin and Janis Joplin I have crashed and burned. It’s all about finding the voice.