One of the easiest things to do is also one of the hardest, and that is to write down that piece of dialogue, turn of phrase, descriptive passage, ear catching name for a character, or any other part of writing.
Granted, it can be hard to write something down when you are driving or in the middle of shopping for food for that big holiday meal, or even in the dark watching a movie. I’m sure you can fill in the line, I had a great idea, but I couldn’t write it down because….
The only thing I can say is I have kicked myself too many times over things I have forgotten when I told myself I would remember them until I could write them.
Sometimes, it helps me to remember the first letter of each word in a phrase I am trying to remember until I can write it down. But I always, or at least almost always, have a pen and paper with me, even a scrap piece of paper. And though I still fail, I try to write it down as soon as I can after the idea has come to me.
It’s not always easy, but nobody said writing should be. Sometimes it is. Often it isn’t, so don’t make it harder on yourself by not having pen and paper or some other way of recording that bit of inspiration when it comes your way. Even if I don’t end up using it, I have acknowledged it, and I have found that acknowledging inspiration helps bring forth more inspiration, while ignoring it or being lazy about it only causes it to go elsewhere, to someone else who will appreciate it.
–David E. Booker
Booker's Blog 