The more you write, the more ideas you are going to generate. It's inescapable; as your brain gets used to being creative, you're going to create, and probably many more ideas than you need. And at some point later, you'll be able to use those ideas. But only if you catch them.
It is essential to get your ideas recorded permanently as soon as possible after you think of them. The longer you wait, the more the idea will fade, and the less will remain when you finally are ready to take it down. This means you have to be able to take your ideas down wherever you are. To help you catch your ideas:
Keep a dashboard clipboard with a small notepad in your car
Carry a small notepad in your purse, briefcase, or pocket
Keep a notebook on your bed stand
Or if you prefer, use a micro cassette recorder
A handheld computer or PDA can also be great for catching ideas; especially when you are in public.
However you decide to capture your ideas, you must do so as soon as possible. Immediately, if you can. This applies even at night--perhaps even more so at night. At no time is an idea likely to be more vivid than at night, and at no time is it likely to fade faster. If you wake up in the middle of the night to a great idea, you really need to write it down. Get yourself a drink of water, jot the thing down as completely as you can, and go back to sleep. In the morning you will be in a much better position to judge whether the idea holds any real promise. This is much better than waking up certain that you had the inspiration for the next Great American Novel last night--and now you can't remember what it was!