Writers write everyday. Every single day. Even if it is only a sentence or two.
You should always have an "open feeling" about your story line.
What I mean, never be completely feel "happy about it", It should always be "could be better".
By going back and back to it. over and over again, you will start to see things you missed, or what could be better.
Rule #3. Don't through away those old ideas. Keep a folder, or file of the stuff you didn't use this time. Save for another time.. these are important.. Honest.