If you write something in the evening or at night, look back over it the next morning. I tend to be less self-critical at night; sometimes, I've looked back at things I wrote the night before, and realized they were no good at all.
Forget the idea that inspiration will come to you like a flash of lightning. It's much more about hard graft.
Routine is really important. However late you went to bed the night before, or however much you had to drink, get up at the same time each day and get on with it.