I constantly feel like I've forgot to do something...

Keep a notepad around. That can help. Even just jotting down words that remind you of things you think you have to do, or things like that, can help. It can't hurt, anyways. If this is specifically for when you go to bed, and want to remember something in the morning (Happens often for me), try to associate the thought with something (It could be an action or something visual).

For example, if I want to remember to take my vitamin in the morning, I may place my glasses on my bedside table in a weird manner. When I wake up, I'll see that, and associate it with my vitamins. Writing on a notepad, as I've mentioned before, helps me a lot, personally, too.

 

If all else fails...have you ever seen the film Memento?

 

I've got ADD, this is my life!

 

i forget things all the time. What I do is "retrace my steps", so in my mind I'll rewind to what was I thinking about before I forgot what I forgot. Then that will lead me to what I thought next. I will think and think until it leads me to what I had forgotten. I've gotten much better at this technique, and have to use it less frequently now.