To remember something. Say it in your mind last thing at night and it will be the first thing that pops into your mind when you wake in the morning.
It works for me
Read something interesting (something as small as a news article or an internet blog or even a solution you read here)and share it with a friend. Not only will you have read but you'll probably have an great conversation, too.
If you can’t remember why you crossed the room or went upstairs, retrace your steps exactly. The action might trigger your memory – if not, don't fret about it. Do something else!
If you were having a conversation and you were about to say something but then you forgot it do this. Go through the conversation you were having and your opinion/contribution towards it then think of how you might have come on to the different topic.
If I wake during the night and remember something important. I turn the clock away from the bed. In the morning I wonder why I've done that and usually remember! Or throw a pillow on the floor. Anything to jog your memory in the morning.
when I have to remember a thing, coming up at night, I write it down on a paper which allways lays next to my bed. Then I am sure I wouln't forget in the morning
Use memotechnics. If you see that you need toothpaste when you are in the bathroom, make yourself a picture of a tube as a stick-man dancing around with a Father Christmas hat on, for instance. You will remember it perfectly when you go downstairs to the shopping list, whereas before I did this, I was muttering 'toothpaste, toothpaste …' all the way down and still managed to forget. Only valid for visual types!