Generating ideas is more about the process rather than the result. For me good ideas are the results of a series of step, rather than one times insights. Ideas came from itinerative process, where one ideas are building from the previous one.
Ideas can came from different types of activities such as brainstorming, sketching, and discussion. What interesting is some times good ideas came when it is least expected. This is because even after those activities our mind are still working on those ideas, when we are doing other things our mind can see things from different perspective. In this change of state our minds see things from different point of view.Taking different approaches and opening up other possibilities.
Sometimes we can see designers do things that are irrelevant to their work. We might think it is useless. However in my opinion, they are trying to change their state of mind. In our group, sometimes we do that also. For example when we are tring to prototype our shapes we dont limit ourselves. Sometimes making somethings that not related to our projects. However this is one kind of state change. So there is no good idea or bad idea. Because each idea can stimulate other idea.