1. Keep a set of notes: Keep a small notepad beside you. As ideas to change the story come to you, jot them down. If there are ways to put that into what you are doing right then, do that. If you would have to go back and fix things previously in the novel, jot that down quickly to remind yourself, and then keep moving forward.

2. After you are done, refer to the notes: During the time you were writing, you may have had many ideas pop into your mind. Now is the time to go through them and pick and choose which ideas you want to use or eliminate.

3. Decide how to introduce the changes: Once you have decided which things to use and which not to use, jot down the details necessary to put it properly into the story.

4. Edit and Implement: Once you have a plan, implementing becomes much easier! I think it goes more quickly, too, because you know exactly what you need to go as you jump into it, and you aren't "winging" it, so to speak.