You don't have to be the best guitar player, or have the best voice, or even be the best looking person - writing a song that moves people is worth more than all the other nonsense. (Just look at Bob Dylan - he's got almost no vocal range at all, but his songs are deeply moving and iconic.) If I had to offer one piece of advice: Write a song that moves people, and write it from within yourself. Your personal narrative is more engaging and moving than anything else you can imagine in your mind.