I used to be able to memorize my tasks, but life has become too busy for that to work for me anymore. I usually write things down on sticky notes. When I'm home, I have a to-do list at my desk, but it sometimes gets buried under the clutter on my desk.
I kept a planner part of the time in college - I had a paper one, and later an electronic one on my ipod. I loved the electronic one, but I got out of the habit of checking it, and it went by the wayside, unfortunately.
Nowadays, I don't have a good system. I'm intrigued by Google Keep, though. I'll have to look into it. Thanks for the recommendation, Clank!