Writing things down also causes some additional thinking to go on so that may give you even more ideas.
Also, when you identify a problem, spend a few moments thinking about why that problem exists, and jot down your ideas. Finding the obstacles is the key to figuring out how to scratch that itch.
I'm pretty lazy and my mind has the tendency to space out into thought, so no matter what I'm doing (programming, yard work etc) I always look for ways to make it easier on me. A lot of times there isn't much to improve and you just have to keep plodding along, but sometimes you get really neat insights and ideas.
For example, some time back I was working as a web developer doing applications for program managers at a large company. After a few months of doing that, it turned out a LOT of the applications they needed were very similar, so after I finished my intern work term and went back to school, I made an application that writes other applications for my 4th year design project.
The idea behind it is that non-programmers can use a GUI to generate a certain class of applications automatically. Turns out that was a very good idea, since while I was writing the prototype Coghead (www.coghead.com) came out with their public beta and their software aimed to do the same thing I was doing (albeit in a different way).
I could give more examples, but being lazy is generally a good source of problems. :)
You can hold a tool in the back of your head, and try applying it to everything, to see if it might fit. This requires discipline. It is often much better to hold a problem in your head, and see if new tools might apply, Feynman used this technique to great effect.
Or you can try to solve other people problems. This requires insight, but it also requires empathy. This is a hard thing to cultivate. It can't be turned on like a switch, and it's difficult to empathize with those far from your life experience. But there are many people who've lived lives similar to yours -- if your friends don't have any problems in their lives, they are unusually charmed.
So don't do that I guess.
That is ultimately how I came to the vision of http://www.propertystampede.com . Ultimately I saw a problem of lacking innovation in the real estate rentals world. So I am solving it.
Chris
Combine that with a solid knowledge of history.