It's very difficult to talk about what makes a good song. Theory can explain why chords and scales work together but can't tell you if the song is any good. Like anything else, good songwriting takes practice. If you're into songwriting instead of soloing, you should try to compose a song every day, sometimes two. After you're done, write it down or record it and stuff it in a drawer for at least four weeks. After a month is up, go back and look over what you wrote. Over time, maybe out of the thirty or so tunes you wrote, you'll find five you like and one really good one. Just like practicing scales, songwriting takes persistence and hard work. You're probably not going to be very good at first, but after a while you'll get more comfortable with the process and you'll be more efficient.

Remember that music is an enjoyable thing. Don't feel as though you have to tackle this book all at once. There truly is a lifetime's worth of information here, so take your time. Study the parts that interest you and give the other ones a chance. Constantly revisit the old material to see how much you've learned and how differently you view it. Above all else, play the music that's in your heart and enjoy the richness that music offers.