When you have ideas it is best to get them into your PBOK (Personal Body of Knowledge) as you have them. At this point, they may not be well thought out, but they get captured and not lost.
The ideal is for each idea to be singular and to stand on its own. This rarely happens at the beginning of an idea. It is therefore necessary to create a practice of continually refining your ideas. As you refine them, one idea will get split into multiple ideas that support each other.
When ideas are refined they can be used in many different contexts. Ideas you have about relationships with friends and family might be applicable at work. Ideas you have about games you play may have relevance in investing.
When ideas are refined they can be assembled into bigger ideas. At the start you are just collecting different ideas, later these ideas can be assembled, they may even be assembled into your next startup.