Ask writers, speakers and other people how they manage to put so many ideas together and the answer is pretty much always the same: I write down ideas as I think of them. Where you write them down isn't so important. I write some in Moleskine notebooks -- I find the solid little books inspiring -- many on scraps of paper and the rest using tools like Evernote. Collectively I refer to them all as the Ideas Box, though this is a conceptual box because they are never all physically in one place.
Try writing down the ideas you have for a week or so then wait a couple of weeks and go back to review them. You will be amazed at how many ideas you had thought of that you had completely forgotten until you read the notes again. These lost ideas are what makes you think you don't have ideas, when in fact you did have them but let them fly away.
Just writing down all the ideas you have is probably not going to make a huge difference because ideas come at times when you don't have the possibility of neatly recording them in your notebooks. A much better method is to write your notes in two steps. When you have the idea write down a brief note -- just keywords if you can't write more -- but then as soon as you get a chance to sit down in peace with the notebook add some more detail so that you will remember better.
If you write s few keywords this is enough to remember the whole story later the same day or maybe the day after, but wait two weeks and those keywords will be meaningless. I know this because sometimes I have forgotten this second step so my notebooks sometimes tantalizing fragments that mean nothing to me now, though one day I thought they were wonderful. On some rare occasions I have managed to recall a lost idea, but some are still a mystery. What, for example, did I mean when I wrote "A grave matter!" Still working on that one, but I'm sure it was a really neat idea.