To-do lists can help a great deal, and it is important to categorize your to dos by importance.
But, there is one thing that takes a higher priority than the to-do list; your calendar. So once your to-do list is done for the day (or week), schedule the items on your calendar. Not only will this make it more likely that you will get the items done, but you will also have a better idea about how much of your day will be taken for each item.
Do you find it difficult to get to sleep sometimes? Do tomorrow’s to-do list before you go to bed. Writing the items down will help get them out of your mind so you can relax better before bed.