Finding a proper list format is crucial when it comes to visibility. Select applications that are catered specifically to your needs. For instance, Things can sync with your iCal so whenever you check your calendar, you will also be given your to-do list for the day. Or, iOS 5's new Reminders feature is quite handy. Set a reminder to call your mom when you get home from work and as you're walking up to the front door, your phone will alert you with a reminder. Alternatively, since so many of us spend our days online, browser-based to-do lists can become quite ubiquitous in our daily routines like Teux Deux (also with accompanying iPad/iPhone app).
Still not helpful? Despite the advanced technology we constantly employ to get us through our day, sometimes the analog solution is always best. We found that taking a notecard or slip of paper at the beginning of the day and writing down all of our things that we have to get done on it was the most useful. We take that piece of paper and stick it in our pocket and don't throw it away or take it off our person until the tasks are done. Sometimes we can finish everything in the morning, other times the paper remains with us until we're ready for bed. Either way its presence is an excellent nagging reminder we don't seem to get from digital solutions.
One last tip for compiling to-do lists is to make your tasks actionable and bite-sized. Don't put "write thesis" on your list. That's absurd and will only serve to further prevent you from getting it done due to its daunting nature. Instead, break down that massive task into smaller actions which you can more easily accomplish. Often times people who can't seem to complete the tasks on their lists suffer from this exact problem. Try to see if you can pick apart your list any further and if that helps you in the completion of your tasks.