An idea is composed of individual thoughts strung together. Occasionally, this string is beautiful but usually it feels trite and we ignore it. The human creativity is at it’s best when it can string seemingly unrelated thoughts together into a wonderfully coherent idea. We see this in good fiction novels where, let’s say, the thoughts of “compassionate aliens from other planets” is combined with thoughts of “evilness of Wall Street banking”. Suddenly, you have a novel idea in the domain of “aliens helping humanity survive itself” (the domain itself, of course, is not novel).
And since thoughts are very likely infinite due to ever increasing information and entropy in this Universe, ideas are infinite too. Which naturally implies that we will never run out of “good” ideas (a subset of infinity is also infinity in this case). Moreover, human memory is limited and we regularly celebrate rehashed old ideas. A little bit of thought into forgotten good ideas can suddenly give birth to a new beautiful idea that appears great in current context. This happens all the time in fiction, music and even in a field as young as computer science.
Now getting access to this infinite pool of good ideas isn’t as simple as breathing air. You increase your proximity to this pool by engaging in activities like reading more, thinking more and having interesting new experiences. But most important of all, you need to develop an appreciation of novel ideas. You have to see them as individual entities in a story or in a piece of music/movie or in science and then notice what makes them stand out. This practice then helps you do the same to random thoughts floating in your head. Most people aren’t even noticing novel ideas that their brains regularly give them a glimpse of.
Be conscious of your own thoughts and appreciate the bizarreness of the most complex thing in the Universe that is sitting right inside your own head. You will be happily surprised that you are much more creative than you thought.