I'm the type of person who really needs a to-do list but is rubbish at maintaining one. I've tried many different solutions: specific apps, pen and paper, spreadsheets. None of them have lasted for longer than a couple of weeks.
Now though I think I've settled on a system that really works for me. I use Evernote ALL THE TIME. It's an essential tool for me. So I thought, how can I use the tool that I already use to help me organise my time.
The key was to format it in an appropriate way. At the top of my list I have the 'week beginning' date. Then I have my current list of to-dos, ordered roughly by priority. I add EVERYTHING work-related that I have to do that is a discrete task, even small tasks. If I do something work-related that's not on the to-do list, I add it to the list. I use the checkbox list type, as it soothes my OCD side to see each box ticked off. Once a task has been ticked off, I copy and paste it into another list below the main list, which has today's date as the heading. So as the days go by you end up with an archive of your completed tasks for each individual day.
Visibility of the list is key. One of the biggest pains in trying to use a specific tool was that it was one more thing to have open on the screen. With Evernote, I just add it to my 'Shortcuts' list. Then it's always there in the top-left of Evernote, a tool that I would have open all the time anyway!
At the end of the month, I'll archive that particular note in a separate notebook, take it out of my shortcuts, and create a new to-do note for the month.
I've now started to expand the format to include other types of to-dos. I often review relevant newsletters and blogs for content as soon as I get into work, but then I like to actually read them over lunch. So I've created a 'Lunchtime reading' list, again with tick-boxes, and a 'Reading archive' at the bottom of the to-do note.
Anyway, it's a very simple solution, that appeals to me for it's 'Collect the completed tasks!' nature.