In its original form (ironically I can't remember where I found it or who suggested it) the idea was to put an orange on the bed as a reminder to do something before going to bed at night. The strangeness of having an orange on your bed is enough to jog your memory about why it's there.
It doesn't have to be an orange. Any brightly coloured object placed in an odd place that is easily seen will do. I have a red heart-shaped fridge magnet which I leave in various places - on the bed to remind me that the rubbish bin needs to be put out, by the front door to remind myself to take something with me, on my chair to remind me to turn off a tap or take a cake out of the oven etc. When I don't need it as a memory aid I put it back on the fridge. It's remarkably effective. What tricks do you use to help your memory along?