As much as we want to progress, 90% of your songs (vocal and instrumental) need to be pieces you can already mostly do, with only a few problem areas, especially at first. You're to move from a position of strength and establish a firm foundation that you really CAN play as you develop fundamentals.
Books, seminars, articles on songwriting are awesome and useful. But the starting point is the song in your ear and heart. Don't reverse it.