1. Write the idea down
2. Put it where you can find it again
3. Use it
How you do #1 is up to you. I can tell you one thing--for all the cliche about writing on scraps of napkins or old receipts, that's probably the worst way. Why? It's harder on step 2. Trust me, I've done the scraps thing. The best way for me to keep ideas I actually want to find later is to write them in a spiral notebook, put them as a doc in my computer or phone (and back them up!) or put them in my anthemion storylines program. I love the storylines program best, because it's easy to retreive.
2. However you get your ideas down, finding them again is the key between a brilliant idea that you put in your novel and the brilliant idea that ends up forgotten under the car seat. Some people have a file. Me, I search notebooks. (You may have seen my joyous tweet about finding some old noted I'd forgotten I had on Discovery.) I should file. The best way, for me, however, is with Anthemion Storylines. This is a simple program. It looks like a bulletin board, and you can post items as an index card, then move them around, etc. When I get an idea for a specific story, I start a new file and toss the ideas there as different cards. Later, I can go back and play with the order until I can write.
When I have an idea for the story I'm working on, I usually put it at the bottom of the story itself, or make a separate doc file and put it in the same folder as the story.
3. Ideas are not much good unless they get used or they spark another idea. Sometimes, an idea can sit for ages; sometimes, it screams to be written right away. I find that it's best to listen to the screams. I get the best stories or scenes from those kinds of ideas, and when I try to ignore them, they just scream louder.
So, how does this apply to Neeta Lyffe? I was in the car, with Rob driving. We were listening to the radio and some haz-bin celebrity was endorsing some embarrassing product. Usually Rob and I remark, in unison, "They must be desperate for money." Well, as you know, Neeta has been sued and is desperate for money. What if someone wanted her to endorse their product? Would she do it? I had my notebook with me, and ended up writing 1000 words before I was done.
Snippet from the representative of "Bottums Up Diet Drinks" trying to convince Neeta to be the next BUDDy:
Once they'd settled on opposite sides of her desk, he opened up his suitcase and pulled out a portfolio. The cover held a collage of different celebrities--most of whom Neeta remembered only from childhood or sort-of recognized from her infrequent television watching. All held a bottle of "Bottums-Up" in one hand and pointed to their perfect waists with the other.
"Larry" jumped into his business pitch. "We at BUDD have always dedicated ourselves to creating high-quality, nutritious drinks that not only help you cut calories but burn fat--"
"I'm not on a diet."
"--We have several lines: Minimize. Stabilize--"
"I'm not getting fat."
"No! Not at all! Like Mr. Bottums said, you're quite fit. Stunning, even. That's what he said. Exact words."
Can you tell this will be a hard sell?