Do you ever read over the work you wrote yesterday, or a week ago and say to yourself - "This is terrible!"
Well, that happens to me a lot. Then I remember the good old days in elementary and high school when my creative writing teachers praised me work. One time I even started wondering if my writing had gotten worse of the years.
So... I dug out some of the stories that I wrote around that time and read over them. Um... yeah... those were terrible. I mean really terrible. Of course - for a ten year old just starting out in writing they were good.
Then I went back and read that stuff I wrote the day before and I was astounded by how much better it was. Publishing worthy it may not be - but I my writing skills have improved.
So whenever you are feeling discouraged - look back at some of your older work and compare it to what you are writing now. Even if your writing isn't perfect - at least you are getting better.