Does It Fit

It is difficult to help you or give advice if with out more infomation about the original story and your new better idea. I would like to first ask do your original idea and your new idea fit together?

If Yes, then reread your original story and take note of how you would be able to incorporate your new better idea into what you already wrote. You will have found that you have written 50 pages of a rough draft. You will probably end up rewriting serveral pages, and find yourself with a better story. Once you 'get back to where you stopped' you will naturally continue on with your better idea.

If No, then reread your story and ask yourseflf the folloing questions. do you still like it? are you statisfied with what you wrote? If the answer to these are no then still be sure to keep it saved, it is still stuff you worked hard on, and you might find yourself coming back to it later. Essentially, your 'junking' your old story, and will start a new book with your new 'better' idea. If you want to stick with your new idea, and finish a book, then try to think about it in sections. Try keeping one scene in your head at a time (this might prove difficult), and write it to your satifaction. Let your mind drift and flow to the next scence with the end of that one. If you continue like this then pop ups for new 'better' ideas for a completly different book will lower, instead you mind will stick with making continually making improving your scenes.

By using this method you can return to you old idea reread those 50 pages, and improvements for your original will come to you.