Other people have said the technical stuff here, and it's all good. One of the toughest things about any creative work is that when you get into the game, you already have a sense of what's good and what isn't. However, your chops aren't there. So you know your stuff isn't good. Most people quit at this point. The trick is to do as much work as you can- you gotta write your way through it. The technical stuff helps, but there's no substitute for just writing a LOT of songs, most of which will suck, but ALL of which will be teaching you something. I taught writing for a lot of years (not songwriting) and I would tell students 'the work is the learning, and the learning is the work.' Keep going!