The following is generic advice. If you can tell us more about how you do thing and all, we can give more specific stuff.
Start with shorts. Work up to a novel. Build up that discipline to stick to a project and finish it.
If you don't outline, outline.
If you do, maybe don't go into as much detail. Give yourself a general direction and a few key points along the road.
You could also set up a rewards system. You set a daily goal. If you accomplish it, you get something you want, do something you want, or whatever. Example: Goal 1000 words a day. Reward: bowl of that ice cream you bought. Could also throw in a punishment like no TV on days you fail.
Main thing is to focus on writing one peice at a time. It's okay to make notes about a story, but you have to finish the piece you're on. Use those other ideas as motivation to complete one project. If you waver, tell yourself that if you don't focus you'll never finish this story. If you never finish this story, what will stop you from giving that great idea the same treatment? Then get back to work. wink